Can two populations of the same species pollinate during different times?
Yes, they can.  Consider an original population that produces pollen over a fairly long time, and then something happens to select earlier &amp; later times for different populations.  This is actually quite common for domestic plants such as fruit trees, where different varieties are selected (by humans) to produce fruit at different times. 

As far as the question itself goes, it's more a case of the other answers being either obviously wrong, or not supported by the information in the question.