It've done this in a few missions and what you need to do is:
On the waypoint for leaving Town A, put a waypoint leading to Town B and in the "Time" box (I think it's called "Time" but i haven't made a mission in ages) type in 900 (number of minutes in seconds) and after 15 mins he'll drive to town A.
For the officer to arrive at Town B, it really depends how far away the towns are. If it's a straight 15 minute drive from A to B then just put the waypoint in Town B like I said, but if it will only take a few mins, put in a couple of waypoints leading random directions and your final one at Town B. This might take quite a bit of working out though.
Sorry if this doesn't help but That's how I did it and it works.