HB31R heavy duty 1800 Watt outdoor plug-in timer is one-piece unit that does not come apart for repairs.
Usually with these mechanical dial timers, when the clock motor starts getting weak, the timer dial starts to stall when tripper meets on-off lever.
And then timers runs slow.
At this point, the little plastic gears are getting stripped out, or the clock motor is overheating.
In either case, the clock motor is spiraling downward.
If this is new timer, take it back.
If this is older timer, the manual and fact sheet do not show a warranty.
New HB31R on ebay for $15
Woods makes 1200 Watt outdoor timer, but lighter weight than Intermatic:http://www.amazon.com/Woods-59204-Weather-Outdoor-Repeats/dp/B0014WRNNK
With larger heavy duty outdoor timers like the Intermatic T-101R outdoor 120Volt timer, you can buy the clock motor separate and replace when clock goes bad. And you can buy the trippers separate. However T100 series timers are not plug-in, they are hard-wired. T-101 is made to last 10-15 years, but cost $60-70. My local Lowes sells them in stock for less.http://waterheatertimer.org/How-to-wire-T104-Intermatic-timer.html#T101