Message box requesting user input if range is NOT empty?

[galvinpaddy]

Good evening happy campers.

I have a workbook (attached)
This records all hours worked in various areas through the business, it relies upon the person in charge of the area for that week to manually enter both the names of all staff, and then the times for each day.
The same person then needs to go to the first tab (named Sign Offs) and add their name/initials into the box relevant to the area they have just added information to. this way we can keep a record of the hours and who has updated them.

What i would like is:

When names AND times are entered into Fridays column (or if the range of fridays column is not empty)
AND
When the save button is clicked
A message/text/user input box (whatever is best) appears that asks for the users name
Click ok
The code then saves the name entered into the relevant box on the Sign Offs tab.

If i didnt explain it clearly please shout and i will re-do the explanation.

Many, many thanks in advance.
galvinpaddy