If your Pothos is still in its nursery pot, then wait for the top half-inch of soil to dry before watering it thoroughly. That is what is meant by watering "as needed."
If it reaches the point that it is drying out about 2-3 days following a thorough watering, then it is ready for a pot one size larger. I have found that to be the most reliable indicator of when to repot. Pothos are non-seasonal and can be repotted at any time of the year.
