How do you know when to pick?

Some are already soft to the touch, but some still greenish and not particularly sweet or tasty... some are still hard to the touch.

Do I need to give the tree more water? Less water?

I know I didn't thin the fruit enough.

It's hot here, we've already had one day up to 105f, though today it is only 90f.

Better to pick em a bit early and let ripen indoors?

Raccoons, possums & wood rats are around, so if I leave them on the tree they are likely to disappear.

Any tips appreciated.

Fruit on any one tree ripens over 10-14 days. I can't tell if any one fruit is a week or a day from picking until the tip softens. So that's my method. Weather and critters may force you to take a different route. In that case you can let them set at room temperature until they reach the stage you want. If picked more than a few days before softening final eating quality may suffer.

One commercial grower in CA picks about 14 days before softening for shipment and about 5 days before for local sales. The fruit I ate in CA wasn't very good but I have no idea how early it was picked or how it was grown.

Mine need to be grown at a long term water deficit to be really sweet. The Honey Royale I'm eating now are divine. I just dried some and they are the best dried nectarines I've tasted, superbly rich flavor. Those were mushy soft when dried. Great dried fruit comes from great fresh fruit.

I had 5 fruits on my tree. First year with it. One fruit fell off before it was ready. I ate it anyways. Wasn't worth the calories lol. The other ones were the best nectarines I had ever had in my life.