the 1pm return is almost perfect. if your flight arrives on time at the tbit terminal, you have to give yourself at least an hour for immigration/customs. then you have to walk to terminal 4. check in and go through security. assuming you get all that done on time, it leaves you with only one other choice, a 10:30 non-stop. if you are scheduled to fly on the 1 pm, you can try going standby on the earlier flight and it's possible you may get on and if not you are confirmed for the 1 pm flight. but what if you schedule yourself for the 10:30am flight but you miss it and now you have to go standby for the 1pm flight? you are at their mercy now and if the flight is full you may have to go on an even later flight.