I'll be in Ireland for a week in May (with my wife and another couple) and just learned that they have no availability for dialysis treatments (until June at the earliest). So I need to make alternate arrangements or cancel the trip. So I'm hoping it is be feasible to fly from Cork ORK to London STN, arrive 8 am take the train to the city core (1-1.5 hours), complete a dialysis session (~4.5 hours), head back to the airport (1-1.5 hours), and fly back in the same day at 8:30. On another day I'd fly from Shannon to London and then back to Dublin. Does this sound feasible? Will I have a wait for UK immigration control at London STN flying from a non-Dublin Airport in Ireland? If so is it long? I'll have about 12 hours on the ground and would need about 8 hours total for commuting and treatment, so it seems like I have enough leeway?