Ticket sites stamp every response with their clock, rounded down to the second. We request it several times, aiming at the moment the second changes, to narrow it to milliseconds.
Your device clock is matched to our server the same way, so a wrong phone clock does not shift the time shown.
The ± value is the measurement error. A slow connection makes it larger; press “Sync again” on a stable network.
Queues and waiting rooms are run by each ticket site. Always check the official notice for the exact opening time.