Hi. Moving this question to a better sub-forum.
I feel I just recently replied to the question of switching jobs right before the application - it is tricky. You need LOR's and your new boss will not be able to provide anything will your old one be willing to write them? (some schools are easy going about the LOR's and allow them from any professional source but some do not and require that they be from your direct supervisor to be considered). Also, you are likely won't get an LOR from your new boss since you will be informing them that you are leaving right away.
However, I would say do what matters for your career as first priority. You may not even need an MBA.
I would recommend getting your LOR locked in now before you submit and leave and that will address most of your issues