Qualifying at most tournaments begins with a sign-in: a physical appearance at a desk by a stated hour. Missing it removes a player from the event.
A draw needs a confirmed field
The draw cannot be made until the exact list of players is known, and every entry that might not appear delays it.
Sign-in converts an intention into a fact. The tournament stops guessing and starts building the draw within minutes of the deadline.
Because qualifying often begins the following morning, that certainty has to be achieved the day before rather than on the day.
Alternates depend on the deadline
Players who did not gain direct acceptance wait at the venue to fill places vacated by no-shows, and the sign-in deadline is when those places appear.
The alternate list is processed in ranking order immediately afterwards, which is why the desk stays busy after the deadline passes.
A player traveling on speculation therefore has a defined moment at which they learn whether the journey was worthwhile.
Enforcement has to be absolute
Exceptions would make the deadline meaningless, so tournaments apply it strictly even where the reason for lateness is sympathetic.
Travel disruption is the most common cause, and players accordingly arrive a day earlier than the schedule strictly requires.
Officials keep a record of the sign-in, and disputes are resolved against it rather than against a recollection of who was present.
The desk is a fixed point in the week
Sign-in happens at a known location, usually near the player services area, and it functions as an informal gathering point.
Coaches and agents use it to make contact, and a good deal of practice arrangement and information exchange happens in that queue.
American tournaments run the process identically, and the routine is one of the few parts of a professional week that looks the same everywhere.
What it means for the qualifying draw
The draw is made publicly soon afterwards, often in front of the players who have just signed in.
That immediacy is deliberate: a draw made in the open, minutes after the field closes, is difficult to question.
By the time the venue opens the following morning, the entire qualifying structure has been built out of a single hour at a desk.
Court allocations and start times follow immediately, since the draw determines how many matches must be fitted into the available courts.
Qualifying days are the busiest of any tournament week for that reason, with more matches running simultaneously than at any later stage.

