Q.lemon trees in pots
I am growing some lemon trees in pots and started them at the beginning of the season I live in NJ). How long should it take to actually see a lemon grow? Years? Plants are maybe 4 inches tall now.

Healthy Lemon Trees can produce fruit in their 3rd year.
If started from seed it will take longer than an established grafted Lemon Tree.
Here is a link with more information.
https://www.gardeningknowhow.com/edible/fruits/lemons/growing-lemon-trees-containers.htm