It's only fair to expect that people who rate a lot of games deserve a quick way to play them. Most default engines support exports to any build. If your web version doesn't work after 72 hours I personally think it is in a spirit of a jam to upload it later as a critical bug fix.

And if your game has very good reasons to be dowloadable only, please, spent 30 minutes and make a fancy page with screenshots and gifs. You already invested 3 days, your game probably deserves some "marketing".