all the control on timing is turned over to you. "Let's do IVF in October or December so we have a summer baby." "Ok, but I'm not doing twins this time!!"
The IVF planning was much easier in some ways than the one time we got pregnant naturally, which ended up happening the same month my wife and I both started PhD programs. That timing made for a hectic 5 years of school.
Best wishes to you and your wife. Such a difficult thing to go through, for so many reasons.