I'm a tad confused since your quoted part contradicts what you wrote after. Time not working on it isn't time spent on it <.<. This is particularly true in a game with more things to do than you could every possibly do. But yes as I stated at the beginning if you are in a hurry to just level it then no don't do this obviously. As someone who levels every job just in case one day and already has a dozen jobs to gear merit jp etc I'm going to be doing that in the recharge time while you still grinding
It definitely does which is why if you using assignments tend to use less imps at lower levels. But yes it's technically a tad slower (unless you do those ones you don't have to leave the coalition at all) though you get that yummy balyd and well don't have to worry about gear or anything