How soon after a TT can you start a diet to get rid of the last 5-10 lbs?

I think if you maintain a good and healthy eating lifestyle after you TT and start exercising on a regular basis when it's recommended by your PS, you should be able to see changes-don't be too hard on yourself though.  You are still healing

You should follow your surgeon's instructions regarding post-surgery care. It is important to do this so that your recovery is not compromised. You should be eating a healthy well-balanced diet and resume exercising after about 3-4 weeks, with strength training and core exercises after about 6 weeks.

If you haven't had your surgery yet, I highly recommend that you get to your goal weight prior surgery to get the best result. If you have had surgery, you should wait until 4 to 6 weeks before trying to diet. Your body needs good nutrition for healing. Be sure to eat a healthy diet and gradually cut back on calories. At 6 weeks you can start exercising, that and a proper diet is your best bet.