Mas Importante : Remember to say several times before the transfer "all follow me". Even walk a few steps to make sure all pets are listening otherwise you'll be back in this thread complaining how you got screwed out of your stuff .Then you'll read a few posts later someone thanking you for the pack horse that went wild & all the great stuff this person just acquired .
You have the normal time that pack animals get before going wild. This varies greatly depending on if their owner is still onscreen with them, if they were fed recently, if something attacks them and no one is around to call guards, etc,... If your standing near them under optimal conditions, the time is roughly 6-7 hours I believe. If you feed them it gets extended.
Your best bet is unpacking them one at a time in a house where they can not escape (if someone/something attack them). If in Fel, I always try to double up walls around them or even temporarily use items that are impassable from the house design menu to block them in the middle of my home.
Good luck with your transfer !