The question is more how often rather than how long. For example, this page:
https://www.gnu.org/software/emacs/manual/html_mono/elisp.ht... takes nearly 15 seconds to fully load for me, but then I can live for literally weeks without having to refresh it (ie. other than on sporadic Firefox restart). That's quite obviously different in the 1/10-of-chapter-per-page style of docs that Rust books seem to like.