Two things with steel that are near impossible to separate are TIME and TEMP. For matrix changes to occur, it requires a given temp, for a given time. An example I can offer is when folks try to do a "soft back draw"..... very often they attempt it with a torch, or with a heated bar of steel, and rely on the "colors" to determine when they are done.
Many times over the years I have had folks who were testing for their JS or MS who tried to use the method(s) described above. In a high percentage of those cases, their blades broke when attempted the 90 degree bent portion of the test...after examining the broken pieces of blade, it's very obvious that there was only a tempered "skin" of about .010-.020" on the blade(s)......they got that little bit of the exterior surface tempered, but beyond that they blade was still at full hardness. (which means the "core" was not converted)
I've done a great deal of experimenting with this over the years, trying to "speed up" the process.
I'm not saying it cannot be done, but it takes TIME at the given TEMP, to achieve. You cannot count on the oxide colors that are visible on the blade's surface. In short, after a lot of examination and experimentation, in general, it takes placing the blade's edge in water (of something to keep the edge cool), and AT LEAST 40 mins of heat application to get the steel's matrix to change all the way through a .250" cross section..... that may not be a "scientific" answer, but that is how it works in a practical application, and I make the assertion based on experience.
Everyone must make their own decisions, but again, it's nearly impossible to separate the TIME/TEMP relationship when it comes to steel.