With a little effort and patience, it's easy to set these to an exact time (within about a minute).
(1) Insert a red pin to shut off the timer at a round hour, about an hour or two ahead of the current time. (If you're doing this at 2:30, for example, set it to shut off around 4:00.)
(2) Advance the wheel past the current time, so the timer thinks it's something like 3:30 or 3:45.
(3) Wait for the timer to shut off, and then immediately unplug it.
(4) Plug the timer back in at exactly the time you set it for (4:00 in this example).
At this point it should retain the correct time until the next time you move the timer, have a power outage, or need to reset the clock for daylight saving time. In my experience the various pin slots on the timer are accurate to within about a minute, and the timer itself might lose or gain as much as a minute per month. But that's still much better precision than you can get without this technique.