There is no time limit when ICO can end. ICO is free to design the project according to the length of time they will run the project. Each project has different times so no one can determine when the ICO ends. It's just that at the beginning, the ICO had a plan that had to be arranged in a definite and clear manner. If the planning has been made carefully, we can find out the ICO estimates are over and for the ICO it should not be far from the time set. This is to avoid disappointment from partners and the ICO still gets complete trust.