Delayed messages

**Is your feature request related to a problem? Please describe.**
Sometimes I remember that I have to write somebody late in the night, and I want to text to not forget it, but I want it to arrive tomorrow.

**Describe the solution you'd like**
Send delayed messages, just like in telegram.

**Describe alternatives you've considered**
Use a reminder and text tomorrow.

The issue body is the only entry point provided and names no files, tests, or implementation locations. Start by clarifying the protocol requirements and semantics for delayed delivery, including how scheduling and recipient behavior should work. Done should mean the feature is specified sufficiently for implementation and validation.

Written by the indexing model from the issue text.