Not since I started following the TOC in 2007.
Chagecha lasted exactly eight chapters, but nothing I can remember that lasted less. No matter how long it takes, the editors would know poll results before the first "official" TOC. Eight weeks, or however long it takes, would be to ensure that all the business surrounding the TOC is taken care of before the issue is out. It would be impossible to have results available for the next issue, fans wouldn't have enough time to return postcards. The net issue would have to go to the printer a day or two after the last issue was released, in order to have copies ready for release on Monday. They'd need to give at least a few weeks for a statistically significant number of postcards to be returned. Postcards are on paper, so votes need to be counted by hand. Then they have to be recounted, at least once. Manga are canceled based on poll results, they better be sure the votes were accurately counted. Editors have to meet with mangaka to discuss the results. Then the editors have to discuss the results together before they decide on TOC order. Everyone involved also has other work to do during that time. Time also has to be factored in for the unaccepted. Even if counting votes should only take three days (hypothetically), they have to allocate five days just in case anything goes wrong. We know it takes time whether that is four, five, six, seven, or eight weeks. Eight weeks has been the rule for a long time. It might not be right, but until better information is available, it is a good standard to keep.