A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Use Data Validation on the cells - for example, select the cells - let's say that the first cell is E6 - and use the custom function
=INT(E6*4)=(E6*4)
That will allow any entry by 1/4 hours.
You can also calculate the hours using time math:
=ROUND((TimeOut-TimeIn)*96,0)/4
like
=ROUND((B6-A6)*96,0)/4
Or to make sure they work full hours
=ROUNDDOWN((B6-A6)*96,0)/4