Every order carries a time-in-force. The common set is day, immediate-or-cancel, fill-or-kill, good-till-cancelled, good-til-date and good-til-time, plus auction-only variants.
Expiry rules interact with sessions. A day-order entered at 9:00 am may expire at 4:00 pm or at 8:00 pm depending on whether your broker treats extended-hours as part of the day, and a GTC order is usually cancelled and rebooked by the broker after a corporate action.
Example: a GTC sell at 60.00 entered before a 2-for-1 split may be adjusted to 30.00 for double the shares, cancelled outright, or left stranded, depending on the broker. Reading the policy once is cheaper than discovering it with real size.
Related: good-til-date, good-til-time, day-order