This system is very common in our region; most township departments are part time and paid on call. The part timers schedule is 0600 to 1800, seven days a week, and from 1800 to 0600 is the paid per call.
Put into place because of the regular problem of finding day time volunteers, we have used it for approx 8 to 10 years now.
A department close by, very small city department, went to 24 hour part time coverage and it destroyed their volunteer program. I like the way our system works, as we have plenty of volunteers to handle responses at night - not to mention, during the day if the part time crew heads out on the engine, we will likely get a handful for other apparatus.
The unfortunate part of it is that there are so many firefighters and medics who make their living working two to three part time jobs. The money might be great, but they live without benefits or much security.