There is quite a variety of timers in use, and unfortunately there are no standards so the details depend entirely on the model. The two most common arrangements these days are:
1. The timer dial has two concentric circles of holes and you insert small metal pegs at the required on and off times. These usually use the inner ring for on and the outer ring for off, but not always.
2. The dial has a ring of little plastic tabs which can be pushed toward the center or the outside of the dial. To select the period of operation, you push all the tabs between the required times to the "on" position. The tabs are most often pushed inward for on and outward for off, but this isn't a hard and fast rule.
In both types, the current time is usually indicated by a small molded line or arrow somewhere around the periphery of the dial. It may be at the top, bottom, or anywhere in between.
If all else fails, you can determine both the current dial position and the on/off orientation of the pegs by a simple trial. Set the tabs/pegs to what you think will give a single "on" period, then slowly turn the dial as if you were setting the correct time. You should hear a small click as the contacts open and close, which will tell you the point to use for "current time." Once that's established, you should then be able to tell easily whether the in or out position of the tabs give on and off.
