I try to get my machines running every 2-3 weeks if weather permits me getting them outside for 15-30 minutes. I let them run long enough for the hydro systems to get hot, hopefully removing condensation. I'm not sure this works as I may think, but they have run with me a long time.
My 8hp wheeled blower is run dry, because it is not used until Oct the next season. But, the mowers will be used in mid- to late- March.