The best time to visit is actually very early morning, or late afternoon when the tour groups have left. Vendors selling Thai food and drinks can be found at the entrance to both sites until around 5.30pm.
The best time to go there is early in the morning because locals usually go when it’s cooler and usually in the afternoon.
Please be careful when you are walking on the edges of the pool. It is very slippery because of high calcium carbonate deposits.