Exactly how you do it is difficult to say, because you don't say how you are storing your data, and where you want to do this data checking.
For example, if it is in an SQL database and stored as dates, then its is a case of a simple SQL query to return the max and min value by group:
SELECT Employee,MAX(TimeRecord), MIN(TimeRecord) FROM myTable GROUP BY Employee
If you are storing it somewhere else, then we would need to know.
Typo: "say" for "don't" - OriginalGriff[/edit]