If you referring to the time taken on a J1 visa - as far as I am aware, no one has completed their FAA Licences ATPLS and converted in the time frame allocated of 2 years.
It simply isn't possible alongside working as a CFI. All flight schools are pressured for instructors right now and they're going to work you hard so that you won't want to/be able to study in the evenings.
If you want to instruct in the States do your JAA stuff first - that is your priority if that's where you want to fly, then you can worry about FAA conversions (JAA>FAA being a easier conversion route) and instructing.