Why use the same field for checking in and out? It will be easier to have one field for in and one for out.
Then subtracting the two fields can compute elapsed time in seconds.
and GetAsTime ( TimestampField ) can be used to extract just the time value.
Phil I would have been relaxed if it was like this, but the problem is this that it is an external database structure which stores the checkin and checkout in one field from where I am getting it into Filemaker and then I have to process it so I can get the CheckIN and CheckOUT seperated.
You'll have problems with that. People forget to check in and check out very frequently. Any system you set up has to check for and handle that possibility.
A relationship can be set up to this table that matches by ID and a date to match to just those clock in/out records for that user for that day. Your script can then loop through those records for each user to popuplate your fields and flag cases where there is an odd number of records. Of course if you have individuals that work a night shift where they clock in before midnight and clock out after midnight, this will require a different approach.
You could also simply sort your records by User and also by timestamp and use a script that loops through them processing each record logging the user in and logging them out, while flagging cases where the interval between in and out indicate that a user failed to clock in or out.