Soaking times employed in the hardening of martensitic stainless steels such as alloy 440C represent a compromise between achieving maximum solution of chromium-iron carbides for maximum strength and corrosion resistance, and avoiding decarburization, excessive grain growth, retained austenite, brittleness, and quench cracking.

For sections 13 mm and under, a soaking time of 30-60 minutes is recommended.  For most parts, adding 30 minutes for each additional inch of thickness is adequate.  Soaking times should be doubled if parts have previously been fully annealed or isothermally annealed.

You can find more information at the following websites:

http://www.timken.com/products/specialtysteel/engineering/tech_info/html/Knife%20Steels.htm

http://www.timken.com/products/specialtysteel/engineering/tech_info/html/T-T%20102.htm

http://www.crucibleservice.com/eselector/prodbyapp/stainless/cru440cs.html

Strangely, Carpenter's website merely mentions soaking, with no associated time.  Perhaps their information is what you have been seeing.  Other than this omission, I highly recommend them, and their website for technical content:

http://www.cartech.com  ;(click on Technical Information)

Heat treat and temper in a vacuum or inert atmosphere if possible. I'm no metallurgist, but the corrosion resistance of 440C can be seriously affected by heat treatment, and my experience has been that surface oxidation, crud & corruption or whatever, caused by exposure to air during heat treatment, doesn't help matters much. Of course this would negate the need for stainless steel foil wrap, too.