I commuted from Mount Laurel to different areas in Philly (Independence Mall, Center City and University City) for many years, and I think you'll find that it takes 30 minutes on paper but probably closer to 45 minutes by the time you factor in traffic lights and getting your car parked---assuming you mean that you need to get on the Vine St Expressway to Broad in Center City and not getting off at 6th Street to Independence Mall. Even leaving at 7 am, it's going to take you 10 minutes to get from Harrington to 295. I'd probably agree that you might be best taking 295 to 70 to the BF bridge at that hour, but coming home I would take the Ben Franklin to 676 to 295 all the way to exit 36 or 40 because rush hour on 70 is exasperating.
Depending on your destination in Philly, you might also consider taking 295 to Woodcrest Station and taking PATCO to 15th.
Hope this helps!
Laura Altobelli, Realtor
Long and Foster Moorestown