It's always been kinda fuzzy and dependent upon the one pulling the trigger. Basically it could be anytime after midnight UTC however based on the avatar for J.Edward it says he's in Central PA.
While it could be he gets sleepy, goes to bed and just locks it up the following morning you would be rolling the dice on that.

It is also possible someone else locks it up because they've been asked to for one reason or another. For example, the creator that month is on vacation or something.

So, yeah, anything after UTC is on borrowed time and I myself have turned in final check ins during that borrowed time so I understand your concern.

It's possible J.E might let everyone know when he's planning to pull the trigger.

We're not usually to worried about last minute updates because nobody here wants to win only because someone missed the final turn in by a matter of minutes.