In the current version, Textra ignores an accidentally scheduled time in the past and leaves the time set as Now. If that's not caught we could send a message now that is not intended to go out, with some consequences.

Examples:
If the time is 11am and we try to schedule a message for today, at any time less than now, the AM/PM toggle should auto switch. Obviously at 11am we're not trying to send a message at 10AM (unless Textra implements time travel).
If the time is 8am and we select 4:00 today, assume PM.
If the time is 8pm and we specify 1:00 today, assume AM tomorrow. That is, always assume that we are scheduling into the future ... not unreasonable.

Whenever the AM/PM is autocorrected, a prompt for "Are you sure?" would be helpful to avoid accidentally sending at a time that might disturb the recipient.