With electric tanks, the timers are essentially useless- the temps don't fall far enough over 8-10 hours to reduce the average heat loss by even a percent or two.
With gas heaters (which are inherently lossier due to the necessary insultion gaps and convection through the center tank heat exchanger) it's maybe a bit more, but "...a worthwhile investment..." probably not, in most cases. (It might be with propane-fired tanks though, due the high cost of the fuel.)
What IS a worthwhile investment is insulating the near-tank plumbing (withing 6' of the tank) to at least R4 with closed-cell foam pipe insulation (including the cold feed an the temperature & pressure outledt plumbing), as well as any accessible hot water distribution plumbing. The cheezy 3/8" wall stuff sold at box stores is better than nothing (~ R2) , but in most instances going with 5/8"-3/4" wall goods (online, or from plumbing supply houses, or Grainger). See:
Sometimes the better solution is the lowest-tech.