I am looking for suggestions on the best possible way to compute elapsed time.

Presently, on the input screen I have chosen to collect in separate fields the start date, time, am or pm, end date, time am or pm. Once the individual fields are provided I want to place the vales into a field type of 'date/time' to compute the elapsed time. I am having difficulty placing the separate fields into a field type of date time. Can you provide me with the syntax necessary to concatenate the individual fields into 'date/time' fields or suggestions on the best possible way to compute the elapsed time?

I chose to enter into separate fields to prevent the user from formatting the date/time as required when entering into a field type 'Date/time'. example to enter 6/1/00 @ 3:00 am the user would be required to type 06/01/2000 03:00 AM. Entering the extra zeros to maintain the formatting requirement would slow down data entry. Is this a correct assumpation or is there a way to format the field for quick data entry into a 'date/time' field? The screen I am designing will be used for time card entry.

Thank you for your input.

Gary