i wanna put some tadpoles in my 90 gallon pond, when is the best time/season (i live in central jersey) and how many should i put in

A 90 gallon pond may not be large enough to prevent it from freezing over in the winter. If you are adding tadpoles that need to overwinter in the pond such as bullfrogs or green frogs, then you don't want them to be in there over the winter. A de-icer would keep the pond open but may actually keep it too warm for proper hibernation. Your pond would be better suited to tadpoles that turn into adults within the same year as when they hatch such as tree frogs, wood frogs, and so forth. Those would be added in the spring (the only time they're available) and would leave before the fall. A 90 gallon pond could support probably 100 tree frog tadpoles but only a dozen bullfrog or green frog tadpoles. My green frogs lay hundreds of eggs in my small tub ponds but only a small percentage make it to adults the next year. I have to move the tadpoles from the tub ponds to the larger ponds before the tub ponds freeze over. I don't know if I answered your question.

thanks, i had tadpoles over the summer from about that hatched and transformed into frogs around the middle of august they were small and looked dark greenish