A sort of "dates" in a column with letters from the alphabet will be shoved to the top or bottom of the list.
Your best bet here is to implement some data validation for the people entering dates. If your users are entering data via a form, you are out of luck for now. Date validation on google forms isn't available yet.
If your users are entering data directly into the spreadsheet,
- Highlight the column or cells where dates are entered
- In the menu bar select tools>data validation..
- Enter the criteria as "Date" and "Is valid date"
- Then uncheck the box next to "Allow invalid data, but show warning"
- click save.
This will force valid date entries and help eliminate a lot of data cleanup in the future. If your dates are always today, or within certain time ranges, you can add additional validations to catch year and month mistakes that fall outside the acceptable ranges.
Can you sort Google Apps Spreadsheets with incomplete dates?
