Problems with setup time

Hi everyone, I’m trying to set up an automated programme that will alert me when pir doesn’t detect a human body during a specific period of time (say between 10am and 12pm), but I’ll only be able to set it up for a specific point in time or for a specific period of time (say four hours) for now… any suggestions please?

I’d like it to alarm at a specific time period for not detecting motion, rather than a specific time or duration.