About 500-600+ hours.
An event alone can take up to 10 hours of honest work, about 5 if you know what you are doing. The text, the items, the FFTpatcher work took way less than events (maybe a 40h?). In order of time consumption, for me, it's :
Map editing > Troublesolving > Sprites and custom animation > Event editing > Text editing > anything else
So, that's so much that takes so much time. Don't start if you don't have time. But I encourage you to help if you're patient enought to help a bit!
The decapitation was one of the quickest event i've done. It took me about 4 hours. I was lucky and got all the sprites position right.
If you want to learn more about event editing, PM me or come to the IRC to chat with the few that know how to do it.