Take a look at the manufacturer, a mallory for example will not match with a singer,
if both timers are the same brand you may be able to swap motors but even then you would need to examine the drive gears to make sure they match. Swapping the motors is nothing. You can also take a pocket knife and crack open the timer motor,get the drive mechanism off of the timer motor. I have had limited success with that however. Most of the time the motor will be ok but the shaft will be stripped. I have oiled the timers and had limited success with that.