My experience has been they will spawn for 6 to 7 months and then go on hiatus for about 5 months and then start again.
Different folks will reports success with differing methods. Since they are naturally seasonal spawners, folks will often attenpt to recreate a dry and then a rainy season in an attempt to trigger them. This can have anything from no effect at all to actaully inducing spawns.
The key is in the tds level changes. I have been very lucky in never having to use ro or do full blown dry/rainy seasons. The most I have ever done is to skip water changes for a couple of weeks and then hit the tank with a big change timed to the onset of a storm and the barometric pressure changes associated with it.
I am personally a big believer in the barometric trigger being the most important factor, the tds change next and the temp change least important. Of course as with spawning most fish, a conditioning diet high in protein is a must. If you are willing to feed live foods, this is the best choice, however I pretty much don't do live and rely and an assortment of quality frozen and dry foods.