All messaging apps should let you schedule texts by default. Sometimes, you need to send a message to a friend or family member, but you don't want them to get it just yet. Maybe they're in a different time zone, and it's too early or late to politely text them; maybe they're in an important meeting, and you don't want their phone sounding or buzzing as a distraction. Either way, a scheduled message can save you: You won't forget to text them later, and they'll get the message whenever you think they should. Win-win.
Of course, this is not a standard feature in all apps yet. Some apps have it, like Telegram or iMessage, and it's a great addition when you need it. Others, like Messenger or WhatsApp, are sorely missing it. While Meta doesn't appear to have any plans to bring scheduled texts to Messenger, it does seem like WhatsApp users are getting the upgrade on the horizon. In fact, you might be able to try it out today.
Scheduling messaging in WhatsApp
As reported by WABetaInfo, WhatsApp is currently testing a new feature for users to schedule texts, photos, and videos to send at a later time. At this time, the feature works even when you're offline, so your scheduled messages will still send even if you don't have a wifi or cellular connection. In addition, the feature is not limited to single chats, as so many new messaging features are. You can schedule texts in both one-on-one and group chats, and all scheduled messages are still end-to-end encrypted.
At this time, it looks like Meta is only testing scheduling messages on WhatsApp for Android. The bright side for iPhone users is that this test is quite limited: Only select users are getting the feature at this time—and, while it's no guarantee, you should enroll in the WhatsApp beta if you want a chance at trying it out early. To start, head to WhatsApp's official beta tester page on the Google Play Store. Here, make sure you're logged into your Google Account, then enroll in the beta. Head back to the official WhatsApp Play Store page, and you should have a new update. This is the beta.
Once you're on the WhatsApp beta, you can check if you have the feature like so: Craft a new message in any chat, then tap and hold on the send button. If you have it, WhatsApp will present a pop-up, letting you cycle through a date and time to schedule your message. (You can choose to send the message in as little as 10 minutes, or as long as two weeks.) When you're ready to schedule, you can tap the green schedule button at the bottom of the menu. You can then tap the contact or group name at the top of this window, then tap "Schedule messages" to manage all scheduled texts in that thread.