How long does it take to bike across Israel?

Well, according to research, it seems you could see the whole country within two weeks. With regard to the safety of cycling in Israel, it seems people already do that, and not just on rare occasions. Cycling in Israel seems to be a normal thing for people there, so I would say it's relatively safe, as long as you know how to cycle. You'll have to be careful though to avoid areas which might not be safe to bike in or to be in at all. So you can bike in groups or as part of tours.