depends on what I'm responding to.

at or around threshold level training blocks, these I build as I go but takes me 2 to 3 months to realize substantial gains

vo2max level training - 3 weeks, then I stagnate

AWC - these increase while I'm training the above, but take me a 3 week focus to really top off my fitness.

then a 2 week taper while sprinkling in all the above, short but snappy workouts.

So, to get to a "peak" for me as a 38 y.o. I've to plan for 8 weeks on top of threshold level training blocks. I havent started this yet as I'm still focusing on threshold and getting the rest while racing, but will probably start in June so that I'm hitting a late peak in August for out district RR.