WMG: Trancers

The "ten seconds" for the watch is only the amount guaranteed by the manufacturer.
If you count, Jack gets over ten seconds each time - the manufacturer yet isn't sure how to stop the amount at a set time yet, so any extra time you get it just icing on the cake, but the fact that you can slow time with it is enough reason to make them. You just can't count on the extra time every use.