If you want to benefit from any form of guarantee on the instrument I suggest you leave the overhaul until your bike is nearly completed (unless it's a repair for an existing bike) as in my experience all repairers give a 'time' guarantee, not a 'mileage' guarantee (which they should)....
In the case of my WB30 for instance, where I got the speedo done early on, the guarantee had already run out by the time the bike was completed.. ...Ian