Some people do it once a week, others 5! You can’t really overdo work like Pilates, as it is low impact and simultaneously stretches you out while developing gradual core strength.
That being said, in general, for most people, twice a week AT LEAST is best. But if you can only come in once a week, don’t let that stop you! Once a week is better than never! And Pilates creates an impression on your mind and body that you leave the studio with…so even if you’re doing other activities, you will find yourself applying what you learned in the studio on a daily basis!