Hi Firefrog,
I want to suggest a basic modification to your approach.
With the setup you have, it looks to me like you will have over 250 seperate sheets at the end of the year. This will be a nightmare to navigate. Simply to find, say, Hobby's records for July 7th once you are into November will be difficult. Just scrolling thru the sheets will wear you down.
I propose you have one data entry table set up similarly to what you have now but with a date column before the clients name. each row will pertain to one date and one client. At the end of the year, you will have over a thousand rows if you average 3 clients each day. Having all your data in one sheet will make it easy to retrieve client or employee data and extract it to different report tables whether to invoice or payroll.
SUMIFS() is all about retreiving info using multiple conditions.
My top table is my simplified version of a yearlong data table. Having gotten a slow start July is my first entry. The formula in week =WEEKNUM(date)
The report table sums total hours based on client and week. I think you can expand this to meet your needs. Let me know what you think.
quinn