We are driving from Seville to Ronda and staying overnight in Ronda. We have a 2 pm winery visit right outside Ronda. Is 5 hours enough to allow for driving plus visiting Zahara and grazelema on the way ? I figured 3 hrs for driving and 2 hrs for checking out the towns.

I would suggest to take the highway to Arcos de la Frontera, then go east from there. Zahara is a jag off the main course and I would add another hour for that drive and stop, just to be safe in getting to your winery visit. Of course, if you find yourself running short of time as you travel, you could nix the Zahara stop.

Your 2 hours stopping time will have to include your lunch as well, of course. And allow time to pick up your vehicle just in case there is a line up.

For just the driving times, I find viamichelin.com generally reliable.

When you get to Arcos de la Frontera, stay down below and drive right around - the views from one side contrast drastically with the views from the backside - your cameras will love it.

If I use viamichelin to map to arcos de la frontera and then Ronda it comes to 20 min longer than going to Zahara and then to grazalema and Ronda. Is it because the roads are windier going to Zahara/grazalema that it may take longer than what it says ? Also need to factor in parking so hopefully the smaller towns won't be as difficult ?

Yes, there are curvy hilly sections. But don't finesse it about 20 minutes here or there - these are average approximate times and, in the real world, conditions on any given day may change them anyway. Go where you want to go.

In Ronda, park here and walk down to the touristy action:
www.mastein.es

If the difference of 20 minutes here or there, or the time to park, are critical to your plans, then one might wonder if you are trying to plan without a reasonable cushion for the unexpected.... Just a thought.

I figure if we are running late in Zahara may need to skip grazalema or spend less time there. We are only stopping for snacks as well since we are eating lunch at the winery.

Lilceeja that sounds reasonable. When you have a vehicle you can play it by ear.