"Are there any chips which don't have to be placed on a table?"

NCV & Cow chips...

"How many must be placed on a table?"

I have heard of as little as a stack (20)...Gene would know the exact number. It could be as little as one.

"How long do they have to be there?"

Once they have been put in play there is no time limit on how long they have to be there. Andy - Las Vegas