If you have a problem with the add-on ‘Time Spent Creating cards’ (https://ankiweb.net/shared/info/1178407876) post in this thread. I would not get notified if you just posted a review on ankiweb.
Yesterday I installed the add-on. I’d need a couple of days to see the graphs. I do use several profiles to split my huge collection. I review them all in a daily basis. If at some point in the future I merge profiles, will the time spent data be merged as well?