It is not necessary for them to be on the bed at the same time. If one leaves before the other finishes the baby-making procedure, it doesn't have any effect on whether they get a baby or not. I have had the dad off the bed and preparing a meal before the mom climbs onto the bed, and she still ends up with a baby. As for your couple's time running out, if they are only 37, the still have 13 yrs to try. Mom can have kids until they are 50, sometimes even a little over. So be persistent, have them keep trying and who knows--they may end up with twins or triplets!

NOTE: If you haven't done it already, do a doctor consult on both of them to see if either or both need Baby Boost.