Assuming you are referring to models, the vote ends when the Wheel is spun. The general way it goes is as such:
1.) On a Wednesday modeling stream, the Wheel is spun, and a model is chosen.
2.) That model is removed from the Wheel, and is put in a temporary buffer zone - if the model gets finished in 3 weeks, then it gets placed in the "finished models" pile; otherwise, it gets placed back onto the wheel under the "models to finish" section.
3.) The vote is ended. The submission with the most votes is added to the Wheel. All votes are reset to zero, and the long-time losers of the vote are purged to keep the list reasonable. All pending models are added for the next vote, and the next vote is started.
4.) The model is built over the next 3 streams. Either 3 streams pass and the model is released in its unfinished state, or the model is finished and released.
5.) Return to step 1, and begin the cycle again.
The Wheel is always spun on a stream. Usually at the beginning of a stream, but sometimes it's spun mid-way through a stream or even at the tail end of a stream. Regardless, though, a model is always given 3 streams to be built as much as it can be.
Note that everything is measured in streams, and not weeks. Weeks where I, for whatever reason, cancel the modeling stream do not count. It's 3 streams, not 3 weeks. They are often the same, but not always.