tbone- that is quite a question and I don't think it has a definitive answer. The length of time from pollen to producing nectar would vary from plant species to plant species. Other variables would include rainfall amounts, rain at the wrong time, temperature, insect damage, soil conditions, amount of sunlight to name a few. Different plants have different requirements for maximum nectar production.
Some plants only produce nectar during certain times of the day.
Pollen being brought in is a good sign of a queen that is laying. They will need all that pollen for food.