First off, really sorry to hear that your lining isn't cooperating! Very frustrating.
I am assuming that you have reasonably regular cycles normally. Since you have been taking estrogen for your lining, your FSH would be suppressed and your ovaries should be quiet. I would say that after stopping the estrogen, you would have to wait for your FSH to rise again in order for follicles to develop, and then wait for ovulation (assuming you still ovulate) and then wait for your usual luteal phase. So it could be a while, I would guess it would take as long as your regular cycle, if not longer. Sometimes the body can take a while to wake up and kick back into gear after being suppressed, at least that is what I have found from my own experience.
Also 10 days of provera sounds like a long time, I wonder what the reasoning is (or maybe its just standard for your clinic). Since you have a good lining already, 5 days of provera should be enough to get the progesterone high enough so that it can drop for AF. Its not like you have to build a lining first. I have never taken more than 5-6 days of provera to induce AF. This would definitely be the quickest route to AF.