That was just a guess as to when to expect new roots. Don't go by the calendar, it's all about roots... when they just barely start (little bumps, ideally less than a millimeter) is the time to repot (whenever that happens). Roots tend to be adapted to their medium. So new roots will quickly establish in the new medium - and the idea of catching them just as they start is to minimize damage to those very fragile root tips. (It is hard to not damage them, but if you catch them just as they are starting, there will be more after you repot. ) In fact, Fred Clarke of Sunset Valley Orchids recommends that when you repot, write the date 3-4 weeks BEFORE on the tag. Next time, you will be able to anticipate the new roots before they even appear which is even better.

This is an awesome tip, thanks for sharing.