i've had a lot of the same kind of questions.
i THINK we're talking about full workouts as being anaerobic. you need some time to transition to the faster paces before getting into a full anaerobic workouts- what we think of as traditional interval workouts e.g. 12x400m(200m jog). i think you can start to mix in some "anaerobic pace" work a little further out than 6-8 weeks, maybe 10-12 weeks, but be conservative. i mix them into a generally aerobic workout- like
2x1k @8k-10k pace(200m jog), 5x200m @1500m pace(200m jog), 1k (200m), 5x200m (200m), 2x1k (200m). . . .
stuff like that. it helps you adjust to the quicker paces, but you're never getting in over your head in the workout. no need to devote a whole workout to 200s or 400s at that point.
i still wouldn't want to do a full anaerobic workout more than once a week during the anaerobic phase. even the 1500m relies mostly on the aerobic system. and you're probably racing more frequently during this period and most races count as anaerobic workouts to me. . . . of course it depends on the distance. and just cause it's an anaerobic phase doesn't mean you cut out the AT and LT workouts. . . .
at least that's my take on it. good questions and i'd be interested to hear what other folk have to say. . . .