My bad. I was under the impression that most search engines are compute bound, but if anything there’s probably a glut of compute for such applications and a market appetite for better results.
Certainly caching is important, especially for Word2Vec or other NLP which you'd want to happen in a separate stage after crawl, but as someone mentioned in a sibling comment, there are some factors that are calculated per-query, which can have a lot of cache misses for novel queries.
So you can run your bulk-recomputing whenever you have spare capacity.
Stale rankings aren't great, but don't hurt that much. As long as your liveness is more frequently updated, so you don't send people to dead sites.