I don't think its really necessary to time all shots Dan. Are you seriously telling me that as well as having to ref one match a night you are volunteering to be timekeeper for 1 match a night aswell? I think that 99% of the time it isn't necessary.
The current rules in the monday league are as follows: (refer to rules & constitution section 3)
Shot timing will not generally be enforced. However, to avoid slow play and ensure matches are completed on time, at the referees discretion, a 30 second warning can be given to a player (not within 60 seconds of the previous shot). The player at the table must complete the shot within 30 seconds, or forfeit the visit (with foul).
So if you are experiencing excessively slow play in a match it is permitted to begin timing. Best practice would be to notify the players that due to slow play timing is going to commence, rather than springing it on a player in the middle of their visit.
I wouldn't! Timing is a royal pain in the arse, and totally unnecessary in 99% of local league matches. It would lead to arguments. We have the option to start timing in exceptional circumstances. Let's leave it at that!