I don't know what the "average" time frame is either, but I don't think that matters much. The main thing is to make sure that your overall health is good, and to make sure it stays that way while also meeting your transition goals. Both the cholesterol and the RBC count are pretty big deals, and it's wise of your doctor not to raise your dose until he's sure that both are under control, since T can raise both of them, putting you at risk for future health problems.
There's a lot you can do, other than vitamins, to lower your cholesterol -- diet and exercise can do wonders, and the recommendations for that are good for your overall health, quite apart from cholesterol. Follow your doctor's recommendations, and the chances are that in 3 months (which isn't really that long, although I know it seems like it), everything will be as it should be, and you can go from there.