How long does the pool keep your coins?
The pool's custody policy in plain words: what a balance is, when it pays out, and what happens to balances below the minimum.
The short version
As briefly as the payout schedule allows. Your confirmed balance is paid automatically every hour once it reaches the minimum payout; the pool is a conveyor toward your wallet, not a place where coins live. There is no account to log into, no withdraw button to press, and no step where you must ask for your own money.
Why a balance exists at all
Two honest delays sit between a share and a payout. First, block maturity: the network itself requires a found block to be buried under further blocks before its reward is spendable, which is why your dashboard splits pending (still maturing) from confirmed (payable). Second, the payout minimum: sending microscopic amounts every hour would waste more in transaction fees than it delivers, so payouts wait until your confirmed balance clears the minimum shown on the site.
Small balances are not lost
A balance below the minimum simply waits and keeps accumulating; it does not expire, get swept, or need activity to stay yours. If you stop mining with a balance under the minimum, it remains attached to your address. Check the current minimum and your balance any time by opening your dashboard with your address.
How to verify all of this
Every payout the pool has ever sent is public on the Payments page with its transaction hash, checkable on the block explorer. Your own dashboard shows your pending and confirmed balances and your full payout history. A custody policy you can verify beats one you have to trust.