how long till 8pm

Assuming it is currently 7:20 PM where you are, there are 40 minutes until 8:00 PM.

If instead it is 7:20 AM in your timezone (12‑hour clock), then there are:

• 12 hours from 7:20 AM to 7:20 PM.

• Plus 40 minutes from 7:20 PM to 8:00 PM.

So that would be 12 hours and 40 minutes until 8 PM.