It’s how long is a piece of string. It just varies completely from model to model and depends what steps the individual manufacturer has required.
That said, there are most likely to be complications with A zwave device that pairs in secure mode. Aeon’s newest line does this, even for their lightbulb. Those can be very finicky to pair. If you search the forums for the individual model you working with you’ll probably find a discussion of tips and tricks for those most recent aeon models.
Battery powered devices of either protocol are going to be a little trickier then mains powered devices because there’s more of a timing issue to make sure that they’re awake.
But other than that, it should usually be pretty easy regardless of the protocol.
If they are pairing easily To Vera my first question is have you excluded them from the vera system to remove the control information from each device? That’s different than just removing them. Until you do that, they will not be available to pair to any new controller, even, for example, a different vera hub.
You can do the general exclude from any Z wave hub, including your new smartthings hub, so normally when you’re having trouble pairing a zwave device, the first thing you do is issue a general exclude on it. It can’t hurt anything and it just makes sure that the device is ready.
Also, if you started a pairing and it failed, sometimes the device does a partial update which then prevents another pairing and the general exclude will clean that up as well.
What are the exact models of the devices that you are trying to pair?