when I taught aqua, I did timed interval training, in other words one move with modifications and directional changes and higher intensity) for 90 or 120 seconds, then a brief rest of 30 seconds, and repeat. I started the class with a five to 8 minute warm-up and ended with a 5 minute cool-down / stretch.
I never did any counting because the class participants preferred to go at their own pace, and that was fine with me.
Hello Shani Rosen,
This seems to be of help, also:
Thank you for this question; I have been approached about aqua classes.
Natalie aka NAPS 2 B Fit.