Were you doing it on your own time? From your described “a lot of effort,” I assume it was not but please correct me if I’m wrong.
If you’re being paid for your time by someone else, it’s fair to notify them how you plan to use a significant chunk of that money before you do it. Unless of course you were employed to _not_ do that.
I am not suggesting explaining a day or two of work. But it sounds like you’re talking weeks.