When does the session close?
The trading day is cut at 17:00 Chicago time. Positions are meant to be flat by 16:45 New York time, but nothing here closes them for you.
The accounting day rolls at 17:00 Chicago time, which is where your daily loss limit resets and where a new session opens on whatever equity the last one left behind.
A real firm expects you flat by 16:45 New York time, Monday to Friday, and trading reopens at 18:00 New York time, Sunday to Thursday. On a holiday with an early close, the early close is the deadline.
Nothing here closes your position at that deadline, and no order is expired for it. Being flattened at the session close is explicitly not a breach at any firm that sells these accounts, so leaving it unenforced costs you nothing except the realism of watching it happen.
A session opens on where the previous one left the equity, never on where the account stands now. Otherwise a position carried across the roll would move its own daily floor overnight.