You might change the sort date on one of the twin (either forward or backward by one day) in order to keep them in birth order. I know this is not the correct way, but it will work and so far as I know it will not appear on any reports.
The information under "More - Misc - Birth Information - Twin" can be set but it is not used anywhere in the program. I do not know why it is there except to satisify a place to record that a multiple birth happened.
You may need to add individual text to the twins to state the birth time etc. as the information added in the birth event is also mostly ignored.