Some have waiting over a year and others have simply got lost in the system while others have got it a few months later. There is no definate time frame and this is why everything except for emergencies should be put on hold for the oath if you have it. If not, you are back in the system that you've been in for so long and no telling how long you will have to wait until they re-schedual you (if you don't get lost in the system).
There is no set time, it all depends on how many people are in the queue for the oath which will vary from oath to oath, so only way to find out how long it will take is to postpone it and wait for an undisclosed amount of time...