Well, once they start, they won't stop - at least for awhile. I've heard that older fish sometimes spawn less frequently or stop altogether.
Mine are in their 3rd spawn I think?
A 4th is probably right around the corner.
Something I've noticed: my female always initiates spawning, and compared to some other species I have kept, there is very little if any courtship. Leia (my female) will drop her tube in less than a day and Bruce (my male) shows up to do his part.
Dont be surprised if you come home to a spawn one day with little or no notice.