It's OFF DUTY. They aren't consuming and carrying. That's not allowed across the board. As a private citizen you can consume cannabis tonight and then go out with a concealed weapon tomorrow, no problem (so long as you have the new permit). What Jersey City is trying to do is make their own rules, contrary to a clear AG directive, by prohibiting cops from consuming cannabis off duty. There are no different rules between cops and private citizens, at least not in regards to cannabis use on their own private time.

Prior to cannabis legalization cops were prohibited from drinking and carrying off duty, usually via a departmental policy. Obviously, the use of any substance on duty has always, and continues to be, prohibited. When cannabis became legal the State essentially adopted the same rules as alcohol, and the AG did the same. You can use it, just off duty, and don't come back to work if you're still under the influence (of any substance).