Can I schedule, pause or cancel the send?

Yes. Sending is throttled (gradual, to avoid spam) and controllable at any time.

1. 1Leave the date empty to «Send» (starts in 2 minutes) or pick a date/time to «Schedule».
2. 2After confirming it becomes «Scheduled»: during that wait you can «Cancel» or «Back to draft».
3. 3While sending you can «Pause» and later «Resume»; or «Cancel» entirely.

Consejo: It never re-sends to someone who already received it, even after a server error: each recipient is sent exactly once.