A turn is 6 seconds. An action is implied to be longer than a bonus action, which is implied to be longer than a reaction, with conditional exceptions. This breakdown therefore was logical, and is the general framework most such questions are answered with on rpg.stackexchange A turn isn't 6 seconds. A round is, and even a round isn't precisely 6 seconds. The rule intentionally says "about 6 seconds." A round contains multiple turns. Turns are assumed to have variable lengths within the round framework.
— Jeremy Crawford (@JeremyECrawford) January 12, 2018
Turns take place simultaneously on the same round as per your earlier tweets, thus they last the full round (afaik this is what the League works with). To answer the original question, ‘about’ must be defined contextually, since the question arises from ambiguity. A turn is an abstraction and is not assumed to last for an entire round.
— Jeremy Crawford (@JeremyECrawford) January 12, 2018
This begs the question of what a turn/action are & what in-world dynamics give both those terms universal logical consistency e.g. what necessary similarity is there between swinging a sword and casting a spell? That’d be up to the DM at that point as it affects worldbuilding. An action is a significant thing you do when it's your turn to act during a round. It's fundamentally a narrative and game categorization, not a temporal one. The game tells you that during a round, you can normally pull off one of these significant things.
— Jeremy Crawford (@JeremyECrawford) January 12, 2018
Further clarification about time in combat: a round in D&D lasts for about 6 seconds. That's a round, not a turn. A round is made up of a variable number of turns, and those turns don't have a number of seconds assigned to them by the rules. #DnD https://t.co/smlSuXgTVh
— Jeremy Crawford (@JeremyECrawford) January 16, 2018
That seems wrong. So if I prone someone until the start of my next turn, that could be 12 seconds or it could be 60 seconds from the moment I did it, depending on how many people are standing around?
Also what about spells with durations measured in minutes?
— Bryan Holmes (@FallenWyvern) January 16, 2018
A round lasts around 6 seconds, no matter how many turns take place within it. #DnD https://t.co/1dpvy4uRL3
— Jeremy Crawford (@JeremyECrawford) January 16, 2018