If you convert the value into a number what do you see?
Try this for several different time values with the same date and compare these to the number values of FileMaker TimeStamp fields for the same date and time. FileMaker timestamp fields meaure date, time in terms of an arbitrary number of seconds and MySQL likely does too, but from a different "0 day and hour" than FileMaker. You can probably convert the MySQL timestamp into a FileMaker timestamp by adding or subtracting a certain number of seconds from/to the MySQL value.
To use a FileMaker TimeStamp field in a calculation to show the number value, define a calculation field that simply refers to the timestamp field by name and select number as its return type.
I bypassed FileMaker and choose to use ACCESS as a front-end using the expression below. Before I investigate the hour conversion in FileMaker using the answer above, is there a more efficient solution as of December 2011? Thanks.