How long would it take to doff armour heated by the Heat Metal spell?

Question

Page 146 of the PHB has the table for getting in and out of armour (1 to 5 minutes to doff, depending on the type).

Now the Heat Metal (PHB pg. 250) says;

Choose a manufactured metal object, such as a metal weapon or a suit of heavy or medium metal armour, that you can see within range. You cause the object to glow red-hot. Any creature in physical contact with the object takes 2d8 fire damage when you cast the spell. Until the spell ends, you can use a bonus action on each of your subsequent turns to cause this damage again. If a creature is holding or wearing the object and takes the damage from it, the creature must succeed on a Constitution saving throw or drop the object if it can.

(Emphasis mine)

I imagine a creature can't just drop a suit of armour it's wearing, otherwise what's the point of having the don/doff time rules, and it drops the object only if it fails the saving throw.
Even if Heat Metal only targets one piece of the armour, the obvious choice would be the shirt/breastplate if you can see it because there's other things a creature would have to take off before that.

So, is the creature trapped in their red-hot burning armour, potentially taking the extra damage for the 1 minute duration of the spell, or is there something I'm missing?

If there's strict RAW on taking armour off in less than a minute, I'll take it, but I'll happily accept answers that simply make sense provided there's an in-game time frame (1 action, 1 round, or whatever) given as well.
As for the type of armour I'm just looking at whatever's in the PHB (chainmail, half plate, full plate, breastplate, chain shirt), I don't know of any specific sub-categories or the exact size and shape.

This is of course assuming the creature tries to take of it's armour, it may not give a damn and take it like a man, but from an RP perspective I reckon it would feel like a brazen bull torture so I'm going with "they try to get out as quickly as possible".

Answer 1

RAW there really is only one option to quickly take off armor: have someone help you.

Getting Into and Out of Armor

The time it takes to don or doff armor depends on the armor’s category.

Don. This is the time it takes to put on armor. You benefit from the armor's AC only if you take the full time to don the suit o f armor.

Doff. This is the time it takes to take off armor. If you have help, reduce this time by half.

The fastest a PC could shed heavy armor with help would be in 2 and a half minutes or 25 rounds of combat.

RAW options to avoid the damage

1. Run away. As I interpret the spell you would still need to be in its range to use the bonus action attack. Running out of range would be difficult to achieve since the spell attack is a bonus action allowing the caster to use both their actions to follow you. However if allies impede the movement of the caster or your move speed is greater it could be accomplished in one round.
2. Deal Damage. Every time the magic user takes damage while concentrating on a spell they are forced to make a CON save to keep that spell up. If everyone hits the wizard odds are pretty high that he will fail one of those CON saves.

Houserule option

Let the PC take it off with a standard action, but doing so damages the armor, preventing them from wearing it again until they have it repaired.

Musings on Heat metal

There is no requirement for a PC or NPC whose gear is affected by heat metal to react taking off their armor. The stipulation of the spell is to throw it if they can, donning and doffing seems to be a bit more than all that and as such I would interpret it to mean weapons should be thrown, but armor can be kept on. I know 2d8 bonus action damage sounds like a lot, but dice only damage has a way of only coming out to be around the average most of the time, while 9 damage a round without an attack roll is pretty nice, it is probably a better idea for the party to focus-fire on the wizard to end it rather than someone in heavy armor taking their armor off and seriously lowering their AC for the rest of the fight.

Answer 2

Xanathar's Guide to Everything provides a new common magic item that seems intended for precisely this situation - Cast-Off Armor.

The descriptive text merely reads,

You can doff this armor as an action.

Much like the standard +1, +2, and +3 armors described in the DMG, Cast-Off Armor can be any sort of light, medium, or heavy armor.

Answer 3

As already mentioned, there is no RAW option to take it fast, that would be suitable in combat.

If you wish to houserule, I would go with my (perhaps limited) personal experience. Below i assume 6 secounds - full round.

• Chain shirt and full chain-mail can be taken off fast. You just need to pull it high and then "bow" deeply, letting it slide over your head. It would require taking off whatever is on it, and it would strip character from any head gear it posses.

  • standard action for chain shirt with nothing over it.
  • full round action for long chainmail with nothing worn over it, or for chain shirt with things like belts on.
  • two rounds for worst case of long chainmail with belts and cloaks worn over it.

  In all cases above chain mail is now tangled with protective gambeson worn under it, and any belts or cloaks, and all that gear can't be used without careful untangling.

• half plate, full plate and breastplate - depends on what is it made of and how is it locked on character.

  • Many historic pieces was locked in place with leather straps. At high temperature leather is brittle (that's what you need to avoid when boiling boiled leather breastplate or shoe soles), so it should be pretty easy to just tear armor off. It shouldn't take longer than standard action, really. Of course, armor is then unusable until someone skilled enough can fit new set of straps.

  • Some pieces sometimes used metal straps in addition or instead of leather ones. In such cases any speed doff would not be possible, but trying to do that might damage armor, making it stuck on character. Unless, of course, your warrior can literally break the metal clamps with brute strength.

Note that, as mentioned by Tony Ennis:

• Plate armors you can take off fast without damaging them do exist. Are they common? DM's call. The lighter armor and "earlier" world, more probable it becomes.
• If magic in your world is common thing, armors designed to fight magic users may be expected to have some emergency mechanism to be sure it was easy to get off quickly. Is it expensive? Does it require reset by skilled crafter? Again, DM's call.

Answer 4

Using RAW there is a rule that you can use to doff an armor PRETTY QUICKLY...

its called Damaging Objects (DMG P246).

OBJECTS

When characters need to saw through ropes, shatter a window, or smash a vampire's coffin, the only hard and fast rule is this: given enough time and the right tools, characters can destroy any destructible object. Use common sense when determining a character's success at damaging an object. Can a fighter cut through a section of a stone wall with a sword? No, the sword is likely to break before the wall does.

For the purpose of these rules, an object is a discrete inanimate item like a window, door, sword, book, table, chair, or stone, not a building or a vehicle that is composed of many other objects.

STATISTICS FOR OBJECTS When time is a factor, you can assign an Armor Class and hit points to a destructible object. You can also give it immunities, resistances, and vulnerabilities to specific types of damage. Armor Class. An object's Armor Class is a measure of how difficult it is to deal damage to the object when striking it (because the object has no chance of dodging out of the way). The Object Armor Class table provides suggested AC values for various substances.

CONCLUSION
Even a full suit of plate mail would be AC 19 with about 30hp... nothing a few good blows will not deal with in 2-3 rounds tops, even more so with adamantine weapons. Once destroyued, the armor will fall off and be unusable and unwearable until fully repaired.

Not sure this is the best option in my opinion...destroying my plate mail and be left with no armor for the rest of the fight, but it is an existing option for someone that really wants to doff an armor quickly....