I noticed that the chief commandants of Kamchatka seemed to serve terms of about five years (Koselev 1802-1807, Petrovskii 1807-1813, Rudakov 1813-1817). Their rank (IV) qualified them to be made regional commandant, and I have no idea how long they spent at rank IV, but they spent five years in charge.
Lots of sources describe decades of total service to the army, but I haven't found anything on the specific appointments making up officers' careers. A few years earlier, Catherine the Great established a rule that civil servants would get automatic promotions every seven years.
Were Imperial army officers' appointments to specific garrisons or companies all five years long?