can thunderbird schedule emails to go out at a specific time

Thunderbird has no such built-in feature, but there's an add-on called "Send Later" that claims to do this. I can't personally vouch for it, but it's reviewers seem to think it works for them. https://addons.thunderbird.net/en-US/thunderbird/addon/send-later-3/ Thunderbird must be running at the scheduled time for it to work.