I've seen something around 4-6 weeks for max anaerobic adaptations (via HIIT or speed work) for primarily aerobic events. I can't exactly recall what Lydiard specifically said... I have the thing around here somehwere though.
Gotta be a little careful with the wording though... max anaerobic capabilities is variable to the event you're doing. For something such as 100m or powerlifting the aerobic base isn't needed at all for the max anaerobic capability whereas it starts to become a factor for 400m and beyond.
Regardles, any type of anaerobic work (and weight training as well) in primarily aerobic races will have to be cycled on/off depending on competition schedule and other factors to peak at the right times. So in reality you have to have some really competent programmers to do this especially with longer race seasons. If you had just one race or goal it's much easier to plan out a schedule to peak for that.
Check out some of Hicham El Guerrouj's off season/competition scheduling to see how they worked in
2. weight training
4. Speed work
5. aerobic base
into his training schedule. It's pretty interesting to see how they planned it out:
Proper programming will have all 5 of these facets within a training schedule. If anyone wants to become a good endurance runner/cyclist/rower/etc. they need to have competent program for all of these qualities. Normally, you just see most people doing the long runs without anything else. They can benefit from added speed work/HIIT/weight training/power work. Likewise,, someone only doing HIIT/fartlek + aerobic base can benefit if they added in power/strength/etc.
So while amateur or intermediate runners can't handle all that kind of volume (and would have to modify programming accordingly.... generally focus on building the aerobic base + getting strong with strength/power work first... the move into HIIT/speed as you near competition and drop volume on strength/power)... you really do need to have some of each integrated with a mostly aerobic base work to perform optimally.
If you've read any of the stuff on advanced weightlifting programming you can see similarities across the different fields. It's quite interesting to say the least. Elite performanc is elite performance whether it's running, lifting, or whatever.