Whenever it gets around to it!

Or, when you can't stick a shovel in any more--

Seriously, in NJ you are on the border of both northern & southern zones--we can overwinter some tender perennials in this state, and we can also have paper birch trees, which deep southerners cannot. This means some winters will "arrive" earlier than others. If you are wondering how long you can plant bulbs the answer is, probably right through November--although doing it sooner gives the bulbs a better start. Many folks even sneak them in the ground in Dec--the daffs won't mind too much but I don't get away with that with tulips.