I'm moving to Nevada in 2 weeks and 6 months pregnant. Can my husband file a petition forcing me to move back? How long does he have to file this?

Short version:  "no."  I have recently litigated this and all the relevant law -- including the New York cases -- says that it is the State of birth of the child that has exclusive jurisdiction over the issue of child custody; if you move to Nevada before the child is born, that State will be Nevada. What may be confusing you is the distinction between jurisdiction and substantive orders.  Anyone with a filing fee can file a motion asking for anything -- including that the other party be made to do something (like move to some other State).  While it is theoretically possible that such an order could be entered, it does not seem likely on the few facts you have revealed. Either way, the 6-month rule that it appears you are being told of concerns gaining a new Home State for child custody purposes, and in your situation, is irrelevant -- Nevada will be the child's Home State instantly if the child is born here. You may want to see the information posted at http://www.willicklawgroup.com/child-custody-and-visitation/, especially the article on the Basics of Family Law Jurisdiction.  You did not say where you did or intend to file for legal separation, but it might not be a good idea to do so in a State where you do not intend to live -- at least until after you have relocated.  Getting good advice in both New York and Nevada should be near the top of your agenda BEFORE filing anything.