Average block time is 15 seconds and if you're doing a 1559 transaction then you can make sure it goes in. Maybe with bad timing it takes two blocks. Due to the random variance in PoW, it can take longer than 15 seconds, but the proof-of-stake chain issues blocks every 12 seconds consistently and the network will migrate to it in about six months.
If you have a full node then reads are from your local disk. If not, there's network latency like anything else.
Of course I will not have a full node. How do I discover the IP addresses of the nodes which maintain the data? How do I keep that set of IPs up to date?
