Some people seem to be unlucky with it. some people say it takes hours...

For me it alternated pretty well, about every save crystal I took there it was changed.

If its rains, talk to weather eye as Renmiri said... he will give ya a time frame. Dry/Rains not too far off... middle of the dry/rains, etc...

Go play around somewhere for 10min or so and come back and check I guess