not OP but on my i7 7700K a fully-featured kernel takes about 2 hours or so to compile. if i minimize the kernel to only the modules i need i can get it down to 20-30 minutes (clean). incremental compiles barely hit 5-10 mins
overall not a big deal, especially compared to something like firefox (or god forbid chromium). or gcc with pgo (which is technically cheating because it compiles itself 3 times if you enable pgo)