Richard,
Generally, "forced air" is not recommended for the 410. Also, ramping down to 400F is normally not necessary, although it should not have any detrimental effects on the steel or the HAZ. Once the necessary PWHT has been fulfilled, the weldment is taken out of the oven and cooled to ambient air temperature. But, let me bring up one more point...The martensitic stainless steels are most commonly given the Subcritical PWHT (1200-1400F for the 410) followed by a Supercritical Full Annealing (1525-1625F for the 410) if maximum softness is required. The full annealing transforms a multiple-phase weld zone to a largely ferritic structure (softer) with scattered carbides. But, in the case of a 410 SS (C=0.15% max) the Subcritical PWHT is the most recognized.
Chuck