When setting up time based triggers it's important to take into consideration if a guest makes a same day reservation after the check-in time. In order to have the trigger fire, you'll need to ensure you have entered the numeric value you want in the highlighted field below.
For example, if your check-in time is 3pm, but you accept same day reservations up until 10pm the day of, you'll want to set this to at least 7. That will capture the window between check-in time and last time to book for that day.
If this is set to 0 and a guest books a same day reservation at 5pm, the trigger will not send (assuming your check-in time is 3pm). This could lead to a late night call or text from the guest asking for check-in instructions.