Wait, you want me to create a webpage that didn't exist before. Sir, we are truly in new territory here; there's no way I could ever give you a reasonable estimation. It could be a day, could be a year! It's very hard to estimate such a monumental task.
If you'd like, Github has a wonderful selection of pre-built webpages that we could just copy and paste onto our site. Like this page for catpics2ascii.js. I realize that it doesn't do what YOU think it should do, but I'm an ENGINEER and you should trust me, I know what's best. WHY DO YOU TRY TO STIFLE MY CREATIVITY?
Seriously though, I think we've all worked with this kind of developer before. The know-it-all that can't get anything done and constantly bitches about all the obstacles holding him back. In my experience, PO's listen to developers much more than any one else. You just have to earn their trust by showing them you can do good work.