During Flower what is the lowest temp allowed for ...

What they can stand and what you should shoot for are too different things but I try to never let anything go much below 60F.. but in nature they get way colder nights than that obviously.. Depends on day time temps too.. you don’t want massive swings from lights on to lights off.

Ideally not more than 10° difference from night to day for best growth and 76° is ideal for lights on, so I don't like them to go past 66° at lights out.

You can go to 25F before the plants will start to die. In your tent I wouldn't go below 55F.