Switching (no pun intended) from warm standby to nonstop switching

[zebulebu]

I'm about to swap my 8212ZL over from warm standby mode to nonstop switching. I know the commands to do it, but can't find anything definitive that tells me whether:

A - there is downtime involved, or

B - whether there is any performance hit when the modules first sync (i.e. straight after the change is made)

Also, is there any guide on how long the change to nonstop is likely to take?

Thanks, in advance