When you are booking multiple journeys with us we'll let you know if a service you have selected overlaps with one you've already added to your cart.
If two services take place at the same time and it's not possible to catch both of them in one day, you will see a warning message that the new trip overlaps with your existing booking.
You will not be able to complete the booking until the overlapping service has been removed from your cart.
If you are wanting to book overlapping trips on purpose (for example, if you are booking travel for two or more passengers travelling at the same time on different services) you'll need to do this in separate transactions.