How does time pass in combat?

Question

In D&D turns are resolved in an order determined by initiative, but is this what is literally happening in the world?

Say you have characters Abe and Ben. Abe goes first and hits Ben with their ax. Ben goes second and stabs Abe with their dagger.

If you were in the game world would you see:

1. Abe attack Ben for six seconds with their ax, and then see Ben attack Abe for six seconds with their dagger

2. both Abe and Ben attacking at the same time

Answer 1

Characters act almost simultaneously

Turns are sequential mechanically, but in the game world they are simultaneous. It is like a battle scene in a movie - all combatants act in the same time, but the director shows this as a sequence of actions.

However, characters' actions are not 100% simultaneous, since one with better reflexes can act faster that another (that can be crucial, e.g. in a gunfighter duel). In D&D this is represented with the Initiative system.

One round lasts 6 seconds

If the spell description says it lasts "for 1 minute" that means the effect will be active for 10 rounds. During one round, every character makes one turn.

"Attack" action is more that just a single weapon swing

Aside from changing their position, normally a character can make one action per turn. An "action" might be an attack. This "attack action" lasts the same ~6 second interval, therefore, it is the character trying to harm his target using his weapon for 6 seconds, not just making a single swing. For the simplicity's sake we assume that during this period an average creature without special training can make a one single successful blow. More experienced combatants might land several hits in the same period - this is what the Extra Attack feature represents.

An example

Say you have characters Abe and Ben. Abe goes first and hits Ben with their ax. Ben goes second and stabs Abe with their dagger.

If you were in the game world would you see:

1. Abe attack Ben for six seconds with their ax, and then see Ben attack Abe for six seconds with their dagger
2. both Abe and Ben attacking at the same time

In the game world it will be a combination of 1 and 2.

During the 6-seconds round:

1. Abe and Ben act simultaneously. They are trying to hit each other.
2. Abe finds an opportunity and tries to land a blow.
3. Ben tries to avoid it. If he succeed (AC was higher than the attack roll), Abe's attack misses.
4. If Ben is still alive, he finally tries to hit Abe.
5. If Abe dodges/blocks/parries the attack, Ben's attack misses.

Answer 2

You seem to be misunderstanding the terms round and turn.

PHB, pg.189:

The Order of Combat

[...] A round represents about 6 seconds in the game world. During a round, each participant in a battle takes a turn.

So a round of combat takes about 6 seconds and within that (roughly 6 second) round, every creature takes their turn. What this means in terms of game-world time is that each creature is essentially acting/reacting all at the same time, within that 6 second time period.

This is, of course, only an approximation. A combat round consisting of 100 creatures might very well represent longer than 6 seconds of game-world time, whereas a combat round consisting of only 2 creatures might very well represent less than 6 seconds of game-world time, even if mechanically, by the rules, a round still takes about 6 seconds regardless of the number of combatants, for the purpose of spell effects/durations and whatnot.

Changing the representation of time in a round of combat based on the number of combatants may not be "by the rules" but there are times when it makes sense (e.g. infinite creatures being able to transport via plants as long as they all take a turn in a combat round).

Even if you're not confusing turn and round; in 'real' time creatures aren't just doing one thing within that 6 seconds either. Even if, on your turn, the only action you take is to attack, that doesn't necessarily mean you spend an entire 6 seconds standing still and attacking in the game world.

Movement and Position
In combat, characters and monsters are in constant motion, often using movement and position to gain the upper hand. (PHB. 190)

Creatures are constantly in motion even if they're not moving out of their space. They're breathing, they're shifting the footing, they're twisting, they're turning. They're doing a whole range of things other than just attacking. How exactly these actions, a creature's turn, or the entire round is narrated in terms of game-world time is up to the player and the DM.

Answer 3

The turns during the same round occur at roughly the same time - that is, within the six-second block of time that comprises a round of combat.

A round represents about 6 seconds in the game world. During a round, each participant in the combat makes a turn. (Player's Handbook, page 189: The Order of Combat)

Answer 4

In tactical combat, a round is the equivalent of six seconds whereby every actor (everyone) takes a turn. A "Turn" is also equivalent of ten rounds or one minute as defined from earlier versions. It's fallacious to conclude that any one actor is consuming an entire six seconds when all actors in initiative have to act during that entire time frame.

Combat is incredibly fast and the most misinterpreted part of tactical time consumption. Please review D&D tactical costs from 2nd to 5th edition which illuminate this clarification.

The purpose of limiting a round to six seconds is to reflect the extraordinary capabilities of your character and the choices needed to be employed in an instant. As players, time is suspended so that the most appropriate (relatively speaking) choice can be made by that individual. As a DM, I always reenact that player's character choice(s) by expository so the feeling of immersion is that more effective, realistic, and gratifying.