Is it good for morning snorkeling (low tide), or afternoon (high tide)?
We snorkeled both morning and afternoon and saw loads but perhaps it is easier to swim in and you don't have to go as far in the afternoon.
Both tides are good for snorkeling. Only depends on if the sea is calm or not. We spend there brilliant moments under the water.
Tides are under solar/lunar control and not as simple as 'morning high', 'afternoon low', so best google ao-sane tide chart and the link to wisuki will tell you when the tide times are in southern Phuket. (I would attach but Trip Advisor doesn't allow links in messages.)
Anyway from what I recall, I think its fine either.
We only went there that one time and it was toward late afternoon. It proved to be a good time to go as we saw lots of different fish not too far from the shore.
I see comments saying high tide is better. So you can avoid walking on rocky stones to get back to the shore
Get quick answers from Ao Sane staff and past visitors.