Need help on Calculating the Percent Ulilization

Hi guys,
I have this dilemma which I’ve been thinking about it for a long time but still not able to figure out. This sound simple but complicated actually (at least for me) so please bear with me. I’ll explain better in the file but this is a brief:

I have 10 stores and I want to calculate the percent of utilization monthly. I give you the time (date and time) of Start/End of each visit for each store. I want the percent of utilization populated on the summary sheet (=hours of visit/total hours of that month *100%)

Thank you so so much for helping me out.