Charge Buffering question

At sonic hurricane one of his exhibition videos explains that Guile (and all charge characters) can run by starting the run animation then charging down/forward during it to then flash kick as soon as its over. When I do it though it takes too long for the down charge so I end up running into my opponent before the charge is ready. Is that normal or is it just really strict timing I need to work on?

From what I can tell, the run has to be really long. AFAIK, flashkick/sonicboom both require a 2 second charge.

I think the reason the combo works is

  1. the sonic boom thrown before the run holds the person “in place”
  2. he canceled the flashkick off of a

both of those help to give enough time to charge the flashkick