Hi -
Just took a 16" round cake out of the oven and it looks great. But...Ive never baked one before so I am unsure how long to let it cool before I flip it out of the pan.

How long?

It's late - can I leave it in the pan til' morning? I used cake release underneath it

I'd dump it out within 20-30 minutes. If you're waiting until morning to dump it, you'll have to put it back in the oven to warm it so it'll release. I hope it's covered so it doesn't dry out.