One note, I have really not found a good way to do this other than just keep an eye on them manually. The services linked below tend to have smaller mempools and lack accuracy to the detail I'd like. Mempool.space is the most accurate place I have found to track fees and that's what I tend to use. I found the ntfy service to be way off on the low side. If you watch fees though you start to see patterns when they drop and rise based on time of day and time of week but there's no hard and fast rules.