Check out how the DS3231 Alarm functions work.

See this article:  Build Programmable Time-based Switches Using a Real Time Clock

The code can be downloaded Here

Check out how the DS3231 Alarm functions work. They will interrupt even a delay() statement. At the appointed time the specified function is called.

This same question was answered here:

How to set Alarms on the DS3231 easily so the Nano doesn't have to go to sleep with delay statements?

For another way to see how to set this up, let me refer you to this article: 

Build Programmable Time-based Switches Using a Real Time Clock

The code can be downloaded Here