How effective is it to alternate build plans? How long do the effects of a given build plan last typically?

My primary focus is crits, because that’s 90% of the racing available to me in my area, so i’m doing the short power build phase, but i have plans to do some longer climb rides next year (I have a goal to do the triple bypass in 2021, which is only a month after another climb focused relay i have planned), so i also want to be working on my sustained power. This got me thinking: Is there any value in doing a sustained power build phase for my next build, or should I wait until closer to next summer to do my climbing focused training?

The core of my question is: If i trained my sustained power now, how long would I benefit from those adaptions? would I still feel their benefit a year from now? 2 years? 5 years? How should I balance my crit power needs with my desire to also be a solid sustained power rider for more endurance focused rides/events such as pikes peak and the triple?