It takes a lot of time for pool to realise miner joined, is that normal?
A lot of time as in how long? It takes a while to generate each block on the pool as it only has about 5GH/s hash power, if that's what you mean. Also, P2Pool uses a PPLNS payment system, and it is handles mining quite differently to other pools, so that could have caused a slight delay, but payments should generally be instant when each a block is found
I stopped mining like 20 minutes ago but I'm still receiving payouts. That means there is some sort of fade-in and fade-out with pool.
Yeah, as I said, it's pretty different to most pools
It uses the Pay-Per-Last-N-Shares System:
Whenever a block is found, payment is given to shares in a window, starting with the last share submitted and going backwards up to some number N of shares. Shares older than the window are not paid. This is essentially a 0-1 cutoff decay function. There is no concept of rounds - shares can be paid even if they were found before the previous block. This means that a given share can be paid more than once - however, the payouts are chosen so that the expected reward is equal to solo expected reward. Because the payment for a share depends only on blocks found in the future and not on shares and blocks found in the past, there is no way to hop based on the current status of the pool. However, if implemented incorrectly, it is possible to hop based on imminent difficulty changes