5040 changes for a full peal are only required if there are 7 or less changing bells (5040 being the extent on 7 bells). For 8 or more you only need 5000 changes. Of course you can ring more (my maximum so far being 7500).
Keeping track of where you are in the peal is the conductor's job - he (or she) is the one who has had to memorise the composition. Usually the comp is fairly regular, so when you get to the same point next time round the positions of the bells in the change tell the conductor where they've got to. (no, I don't conduct!)
My quickest full peal: 1hr23mins
My slowest full peal: 3hrs 45 mins
And here is a Blue Clicky for the song mentioned above.