Sort a column that uses a formula to provide a datetime correctly

This might be a tough one, and I'm not sure there's a solution.

This file is used by sales people to track outbound sales attempts.

I have a formula in Column C that will return a datetime stamp whenever cell B is edited. The goal is to make sure date/time is uniform and accurate and save the sales people from manually updating large lists.

When they make an attempt, then edit cell B and a NOW() timestamp will auto-populate in Column C. It's pretty handy and doesn't require VBA. Dates stay put even when the file is closed/reopened.

time1.jpg

time2.jpg

My problem is sorting. When there are blanks in some rows the only option is it gives me is A-Z. I need to be able to sort Oldest to Newest.

Any suggestions/clever workarounds/helper columns I can add would be appreciated, thanks everyone.