If you scheduled a future start time and then need to make a change, you can cancel the scheduled launch as long as it hasn't started yet.
How
While an election is scheduled, a banner confirms the exact start time and timezone it will launch at, with a Cancel scheduled launch button. Clicking it returns the election to draft — you'll see "Scheduled launch cancelled — the election is a draft again."
What that undoes
Cancelling stops the automatic launch from happening — no invitations go out. Because the election returns fully to draft, the ballot is unlocked again, so you can edit questions or the schedule before launching again. (The voter roster doesn't require cancelling — it stays editable while the election is scheduled.)
What it doesn't undo
If the scheduled start time has already passed and invitations have gone out, the election is already running — cancelling isn't available at that point. Close it manually instead if you need to stop it. See Closing an election.