Can you take your free "use an item" action between weapon attacks?
— (((Eddie))) (@abracadocious) May 11, 2018
On your turn, you take your free object interaction as part of your move or action. It's not a discrete process. See "Other Activity on Your Turn" (PH, 190) for more information. #DnD https://t.co/XyOKUu8lkl
— Jeremy Crawford (@JeremyECrawford) May 11, 2018
Cripes, Crawford. Really?
Yes – you take the free object interaction as part of your move or action.
But the question you are being asked is this: if you want to take the free object interaction -as part of your Attack action-, when during the attack action may it happen?
A Fighter with Extra Attack takes the Attack Action, which allows them to take a free object interaction – let’s say, opening a door.
Can they open the door, and then make their two attacks? Can they make their two attacks, then open the door? Can they make one attack, open the door, then make another attack?
Basically, can it happen at any time during the move or action, or does it follow the new “pre-condition” paradigm of bonus actions, and can only occur last, at the conclusion / completion of the attack action?
As part of the action means it can happen at any time during the action so all 3 of your scenarios will work.