Brent,
The example for addHours in the documentation is as follows: addHours(dateTime(2007, 1, 1, 1, 1, 1), 25)
However, in your case, it seems like you have an attribute that is already a datetime value, lets call it $Meeting/StartDate. So for this, you would use addHours as follows: addHours($Meeting/StartDate, 2) This would add 2 hours to the start date. the dateTime(2007, 1, 1, 1, 1, 1) function call will take those integer arguments and return a date (Jan 1 2007 in this case.
Hope that helps,
Mike