I agree with PP. It depends on how you plan on getting to Chef Mickey's. If you are driving yourself, you should be in your car heading out of the water park no later than 2:00 pm (maybe even 1:45 pm to deal with any traffic, getting a parking spot at CR, etc.). You could also uber or lyft and, again, be in the car by 2:00 pm. You will need time to change, so you probably need to be done with the slides by 1:30 pm at the latest. For us, that would be plenty of time at the water park. We typically show up at 10 am, do slides until 1 pm (the crowds and lines start to build late morning), eat QS there and then leave.
If you are using Disney transportation, it takes much much longer as you have to take two buses. I would allow yourself at least 90 minutes to get from a water park to CR if you are using Disney buses, which would mean only having about 2.5 hours at the water park. That wouldn't be worth it to me.