Totalling grouped values

Hello

I need to calculate the total amount of time under my "time conversion" heading by each of the names in the "User" heading field so that it shows the total usage time per person but I'm having difficulties with this as each user can have multiple entries (as per my attached example)

Also this data is subject to change on a daily basis as the report data is sent to me every morning so the same person may or may not be in that day

If my instructions are confusing please let me know and I will explain in greater detail

Please help

Thanks

Dan