If a linked order, you'd generally see both for the same day. We'd book lines for the morning slot (AM) and the linked FTTC order for afternoon (PM) to avoid the potential situation of the fibre engineer getting there and no line is ready.
The only instance where the dates can be different is where the line is booked and the second order isn't placed quick enough or there isn't an engineer slot on the day to match it so the second order (still linked to the first) is done on a different day.
Matt