I'm on iphone. Just googled it for ios but I can't get it to work. Seems easier on the pc. I use Textmarketer with aworka.
Depends on your OS version
iOS 18 and newer:
Open the Messages app and start a conversation.
Tap the + button and then select Send Later.
Choose your desired date and time, type your message, and send.
iOS 13–17:
Open the Shortcuts app.
Go to the "Automation" tab and tap New Automation.
Select "Time of Day" and set your desired date and time.
Tap Send Message and compose your message, then finish the automation