Editing entries in contests
The answer is YES, oh absolutely YES, you can edit as much as you want whenever you want. If you can clean up your Instructable, add more useful detail or information, or add a video, then go for it.
There are a couple of reasons for this. The big reason is that the project itself, whatever was built or done for the entry, is not going to be changed by these edits. Any change will be to the presentation of that project.
Of course, we also don't recommend publishing and entering an Instructable that is in disarray and making it whole over the next couple of days. It's always helpful for you to make a good first impression.
The other reason that we're fine with edits is that we want authors to see each Instructable as a living document. If you realize that some information is incorrect or could be clarified, then you should be free to go in and make a change whenever you want. Many of these changes are brought about by comments from others right after publication and we don't want to hold you back from that.
So I hope that clears things up for authors and if you have any more questions about it, feel free to ask away in the comments.