No, an index wouldn't be updated the moment you want to use it. I notice when locate and man perform their updates because my computer is busy while they do. Granted I think it is low priority but I still see the result in btop (or any other system monitor program). find isn't quick unless I repeat the same search and the directories are cached.
I am not complaining about spending time on i/o and processing to make an index. I merely stated that it does take time. I didn't think Windows' one was worth it when I last used Windows so I would always disable it but I haven't done likewise on linux.