Hi
It’s easy to build a clock, but a lot harder to make it go!!
Check the running time accurately for a few times and see which gear tooth is a little sticky.
If you start running from a constant point, you could use say 12 0 clock for instance, you should be able to work out how much each wheel has moved. those that have done more than one turn are probably OK, then put a pencil mark where the meshing points are when it has stopped.
Other things to check are the pinions are not binding and have free sideways movement.
I hope this puts you on the right track
Regards
Keith
Leeds UK