When choosing to roll a die as part of resolving a crisis card, must a cylon player wait to allow human players to play a Strategic Planning card, or is the Cylon player allowed to act quickly enough to prevent any reaction to his choice?

No everyone must be given a reasonable amount of time to play interrupts. The same goes for the Humans to wait for an unrevealed Cylon to play calculations or Strategic Planning on a die roll to damage something to.

Source?

Though there is no real source per say Rules or FAQ it is assumed to be sportsmanlike to wait and not be unsportsmanlike about it.

Well if you was on the other end of said trick by a nasty unrevealed Cylon I'm sure you would like to have been given the chance to play that last Strat Plan before him activating FTL and losing on Pop. Its been played that way in our house for a few years and if you head over to Vassal and play online, or even PBP Forums there are a lot of players that will have the same view.

The UFAQ has an extensive timing/sequence chart and I believe that is where it references the requirement to allow "allowable" actions... Startegic Plannings, Cards before skill checks, etc... We usually set some ground rules... like stating out loud before you roll, and asking if cards need to be played before Destiny goes in the check.