The rest period between sets should depend upon a couple factors. One is the goal of the your training program. If strength is your primary goal rest periods of at least two minutes should be taken. In fact if you are training for maximal strength 3-5 minutes of rest between sets is suggested in order to allow the central nervous system to fully recover. If muscle mass is the primary goal rest periods should be in the 60-90 second range. If muscular endurance or fat loss is a primary goal you may want to take your periods down to 30-60 seconds between each set.
The second factor that should determine your rest periods is the selected exercise. For instance, a set of weighted chin ups is more physically demanding than a set of concentration curls. You know that funny looking exercise where you sit on the end of a bench and stare at your biceps hoping that it’s getting bigger? So you would probably want to take more rest between sets of chin ups than sets of biceps curls. The more physically demanding the exercise is, the longer the rest period you may want to take.
Now that you have an understanding of theimportance of your rest period and how long they should be, are you going to track them? It’s not that hard. Just pick up a cheap digital wristwatch or stop watch. You do not need anything fancy. Something that just tells time. Personally, if I do not work out with a watch on I feel out of place. I hate staring across the room at the clock on the wall, if there is a clock on the wall. In the case there is not one available I’m left guessing about my rest periods. And any time it comes to guessing in regards to your training I think you are headed down the wrong road. Every part of your training should have some reasoning.