Every 10 minutes on average. Sometimes the block time is a few seconds, sometimes it is over an hour. You cannot assume a block comes every 10 minutes when considering a fee.

This is the wrong graph to use. This graph shows the number of transactions, but blocks don't include a maximum number of transactions; they include a maximum combined weight (or size) of transactions. A block could contain 1 transaction which is 4 vMB, or it could contain 10,000 transactions of 400 vMB each. If you choose a fee which puts you 50 transactions from the tip of the mempool, you have no idea if those 50 transactions represent 50,000 sats which means you will get confirmed in the next block, or if those 50 transactions represent 50 vMB which means it will be days until you get confirmed.

The graph you want is this one: https://jochen-hoenicke.de/queue/#BTC,2h,weight. It shows the mempool in terms of weight/size. Each block will take a maximum of 1 MB off the top of that graph.