I think it is very beneficial, to have some time between the degrees, to "absorb" the lessons. The exact time, varies with the individual. I was in Indiana (2008), and the GL of Indiana, leaves the time frame up to the individual lodge. If the "coach" of the individual is satisfied, that the man has completed the degree, and has properly absorbed the lessons, and is proficient in the degree, then the man may proceed to the next degree. This policy ensures that the man has the lessons in his mind, and is not rushing things.
I still am 100% in favor of having an accelerated program in special circumstances, such as a military man, deploying overseas.