Arranged a day trip with another family. It's a 3 hour trip for me and a 2hr 20 journey for them. If it was just us I would plan to leave in the morning and spend as long as possible there. So I said we'd leave at 1130 and they would join us as we go through the city where they live and we would take a picnic for the train. They've now said they want to leave after lunch meaning 6 hours travel for max. 4 hours at the attraction but probably 3.5 as they don't want to be back on the late train. I'm sure my DC will want to spend longer than 3.5 hours there.
As I already said we would meet up on the train for lunch and travel together, how bad would it be for me now to suggest we travel separately and meet there?