I wait about one month to six weeks before I think about writing a review for a new toy here at EF (on my blog? that is a different story and depending on the toy itself). And then it could take up to six months to a year before I sit down and actually write the review here at EF. The few times I have written a follow up review the same day, or under the two month period, I do mention the length of time I've had the toy.
As Gracie said, if I read a review that was written under six weeks after the review, I question if the author of the review is still in the honeymoon phase, unless otherwise stated in the follow up review that they have had the toy for a prolong period of time.