I'll be upgrading our Powerdns install on Wednesday. Because our system is redundant and I'll only upgrade one node at a time, I don't expect any service interruption. As always, though, unexpected mishaps may cause brief service interruptions. Most likely these interruptions would be confined to new VM creation, but in the worst case there might be short periods of total DNS failure.
I plan to start the work at around 17:00 UTC (that's 09:00 in San Francisco) and the total upgrade will take an hour or two.