First, CLV P-Chain does not have staking feature, only CLV M-Chain has.
The minimum amount to stake is dynamic. It can move up or down depending on the nominations and the election solutions. Nominators with a stake smaller than this amount may not currently be receiving staking rewards.
About 6 hours
Next ERA, which means the maximum is 6 hours
It's distributed by ERA, anyone can make the claim at any time, while CLV will also claim for user once every day automatically. The reward will not be slashed.