I have found that I use the toy, on average, if it's an assignment, for at least 1 or 2 weeks or 5 to 10 uses or more, which ever seems appropriate for the toy. There are some toys we have owned and used for months or even a year or longer before I feel I know the toy well enough to review. (The Sports Sheets cuffs and tether set was one of those. I wanted to get everything out of the toy I knew we could before writing a review. Also, it's not an every day toy for us, so I wanted a number of uses before writing a review on the toy. It's a very versatile toy and has many ways to use, so I felt we needed to use it in as many ways as he and I could think of before talking about it to other people.)
I don't think for most things, you can't do a good review after only one or even two uses (again, unless it's a one times use item, then you have to go on that one time.) I have had some toys that I have waited literally months to review, because I didn't use it much or I didn't get full use of the toy after a few weeks.
Like Carrie Ann has said, sometimes our first impressions are false. "Wow, this is the best toy ever!" or "This toy sucks." Only to find out after a number of uses, we learned to use the toy properly and the learning curve kicked in so we can write a proper review.
I have a butt plug that I hated when we first got it, years ago. I am just starting to like it now, and I will refuse to write a review on it until I have gotten full usage out of it and learn the toy thoroughly.
Some toys I simply don't write reviews on. My Hitachi for example. Really, is there anything I can say that hasn't already been said? Maybe if I find some really imaginative use for it, but as it is, we use ours for muscle aches first and occasionally sex. Not much that anyone else hasn't already said.