Do you let the turntable spin when putting down record and attach the clamp.

The power is aways on.
One cannot fasten a reflex clamp without stopping the rotation.
Reset AT pickup, place record, place clamp, brush diamond with Stylast. Give clamp a spin (to save the belt from dead start on a heavy platter), hit the on swittch and drop.
Rinse and repeat.

If your turntable is delt-drive you can damage it this way.

If it’s Direct Drive you can’t damage it, and you can change record and add/remove disc stabilizer on top of the record on the fly (with spinning platter if you like).

I press the stop button each time I change record. I put my disc stabilizer on the spinning platter (after I turn it on, not before). But I use ONLY direct drive turntables.

I don't think I want to attempt putting the periphery ring clamp on my VPI while it's spinning. With my direct drive turntables, I leave the power on but stop the platter from spinning when I change records.

Platter is always spinning for the session. No clamps or weights.