TL;DR

Using the Beeper Desktop client, you can schedule your messages beforehand. This will allow you to send messages at the exact time you want your contact to receive them or, as Eric does, trick your family and friends.

How to Schedule Messages on Beeper?

With Beeper, you can automate chat skills by scheduling your messages ahead of time. Currently, this is available on Beeper Desktop. The app does not need to be running in order for the message to be sent in the future. 

This is as easy as going to Beeper Desktop and typing the message you want to schedule. The only difference is that instead of clocking on Send, you must click on the Schedule Message feature.