The only reason for the time based automation rule to not work is if the conditions do not match during the time of execution (once every hour). Since we will not be able to identify when exactly this automation rule runs in the helpdesk, we will have to set an upper and lower limit for the time when it needs to be executed. 

If you want to send an email to a customer 24 hours after the ticket has been Resolved, then you will have to set the conditions as given below:

In tickets > If Status > is > Resolved.

In tickets > If Hours since resolved > greater than > 24

In tickets > If Hours since resolved > less than > 25