Earlier this month, WhatsApp started testing scheduled messages with some beta testers on Android, after the feature had been in development since at least February. Now it's making its way to iOS too, rolling out to some users of the WhatsApp beta for iOS version 26.42.10.19 from TestFlight, with more people set to get it over the coming weeks.
It works the same way as on Android. Once you've typed your message, tap and hold the send button to bring up a date and time picker, then confirm with the green button at the bottom, which shows the exact delivery time. The earliest you can schedule a message for is 10 minutes from now, and the latest is two weeks ahead. The message will be sent at the time you set even if your device is offline then, and the confirmation that shows up in the chat is only visible to you.
Scheduling supports text, links, photos, and videos, though you can only schedule one photo or video per message, by tapping and holding the send button in the drawing editor. Scheduled messages are end-to-end encrypted, and they show up in a dedicated section in the chat info screen, where you can delete them at any time before they're sent. The recipient is never notified if you do that.
In group chats, a scheduled message only goes to the people who were members when you scheduled it, so anyone who joins in the meantime won't get it. It's still unclear when scheduled messages will be available to everyone, on either iOS or Android. It might take a few more weeks of testing and ironing out kinks. We'll keep you posted.