Enforce/Validate cell format

Hi,

I am working on an s.s that will allow operators to enter the time they started and finished a task. The s.s will calculate time taken and productivity with the info entered.

For where the users will enter the time, the cells are formatted as [h]:mm. Because I won't regularly be checking the data they enter, I need to make sure that the data is exactly in the above format as any other format will corrupt my data (and other formats are possible such as a hh.mm instead of hh:mm which gives a completely different result)

I need to restrict the data entered to the above format only and would like to have an error message or some kind of block that will tell the user they are entering the wrong format and not accept the data entered(similar to the error alert in data validation)

Your help is much appreciated

First select and format your cells as desired
Then select Data validation - Time and enter start time as 00:00:00 and end time as 23:59:00