Excel tables or formulas for data analysis

I have a data set of all our inbound calls from last week and what times the calls came in. To be able to monitor when our peak periods were, I want to create a pivot or table that tells me how many calls we got last week in each 15minute time slot. for example, this is part of our data set;

and I want to be able to put the data in here (below) for how many calls last week came in between 7.30 - 7.45 for example.

Is there a formula I can use to pull this data into the cells? or can someone help to create a pivot or normal table?

Thanks!