it depends ,varies greatly,pools have different hashrate and different luck
on average, a block is found every ten minutes,so a pool with 25% hashpower would be finding blocks (in theory,of course)
every 40 minutes,roughly ,once again:you can be finding them more often or don't find at all,if you are a tiny pool
pool hashrate and percentage distribution you can find,for example,here:

https://blockchain.info/pools