I also do my own zinc plating, a tip with spokes is to use a long vertical tank, I use a length of 100mm PVC pipe (sewer or stormwater pipe) sufficient to cover the length of the spoke/s, this way you don't need huge quantities of electrolite fluid or a setup that takes up too much space. Also don't plate with too much zinc deposit, it can cause the threads to become tight with the nipples, not what you want when relacing spokes.
Also use a blue dip (pasivate) for the spokes and a yellow dip for the nipples, gives the off the shelf look.
Typically i would do one spoke at a time, maybe 2-3 minutes per spoke. As Mike52 said, it takes a while to do a complete set, good way to spend a wet Sunday afternoon...
Pete