I think you need to provide a bit more detail. How do you specify your script parameters? Do you have 6 buttons, each with a different parameter? Do they pass a field name to the script?
If so, this script should work:
Set variable [$FieldName ; value: Get ( Scriptparameter ) ]
If [IsEmpty ( getField ( $fieldName ) ) ]
Set Field By name [ $Fieldname ; Get ( Currentdate ) ]
Note 1: GetFieldName ( Table::field ) is a good option for passing a field name as a script parameter. With this expression, you can rename your field in Manage | database | fields and the script will still work.
Note 2: You may want to use get ( CurrentTimestamp ) instead of separate uses of Get ( CurrentDate ) and Get ( currentTime ). This makes it possible to subtract time in from time out to comptue elapsed time and not have to worry about cases where time in was before midnight and time out was after.