How long does the additional fire damage of an oil flask last? [duplicate]

Question

Here's the description of an oil flask:

Oil usually comes in a clay flask that holds 1 pint. As an action, you can splash the oil in this flask onto a creature within 5 feet of you or throw it up to 20 feet, shattering it on impact. Make a ranged attack against a target creature or object, treating the oil as an improvised weapon. On a hit, the target is covered in oil. If the target takes any fire damage before the oil dries (after 1 minute), the target takes an additional 5 fire damage from the burning oil. You can also pour a flask of oil on the ground to cover a 5-foot-square area, provided that the surface is level. If lit, the oil burns for 2 rounds and deals 5 fire damage to any creature that enters the area or ends its turn in the area. A creature can take this damage only once per turn.

The description provides a duration that oil burns while poured onto a surface, but not for oil that's lit while splashed onto a creature. Does a creature covered in oil take the additional 5 fire damage every time it takes fire damage for the one-minute duration until the oil dries, or only the first time?

5e is usually pretty literal about this, and it doesn't say 'the first time the target takes fire damage,' so I'm inclined to think it's the latter. But that seems pretty powerful for adventuring gear that costs a single silver piece, even if it does take an action to set up.

Answer 1

The fire damage due to burning oil lasts for 2 rounds.

before the oil dries (after 1 minute)

As per the description, the oil takes 1 minute to dry, which would take much longer than being burned up.

If lit, the oil burns for 2 rounds and deals 5 fire damage to any creature that enters the area or ends its turn in the area.

This is the important part, since it tells us how long the oil burns for in the area of effect, which being covered in oil would count as.

Practically, standing in burning oil and being covered in it are a little different, in that being covered would be more damaging, but as this sentence indicates:

On a hit, the target is covered in oil. If the target takes any fire damage before the oil dries (after 1 minute), the target takes an additional 5 fire damage from the burning oil.

Mechanically, 5e treats them the same. So a creature covered in the oil and ignited would take 5 fire damage for 2 rounds. (or maybe 1 if they manage to get the fire extinguished, though I would have to doublecheck the rules to be sure).

Further, as stated in the description, the damage can only occur once per turn from the burning oil, which means it is not additive upon itself, so the creature would only expect 5 damage from the oil each turn.
Final thought: the damage should only be applied during the turns of the creature which caused the burning oil, as this would prevent excess damage, and would line up more closely with the 2 rounds statement.

Answer 2

I think you are overlooking a key part of the description of being covered in oil.

If the target takes any fire damage before the oil dries (after 1 minute), the target takes an additional 5 fire damage from the burning oil.

It at no point says that this affect disappears the moment it takes fire damage. Rules as written, if you continue to deal fire damage to it each turn before the minute is up, it takes 5 additional fire damage. Though it says from the burning oil, this is not a burning effect from say Pathfinder. It only takes the additional fire damage if it takes more fire damage from another source, and this can only happen once per turn. So you can't dual wield or extra attack with a torch and get the bonus multiple times in one turn.

It's quite simply an effect that lets you deal 5 extra fire damage once per turn if you deal fire damage to the creature with a duration of 1 minute.