Hi @GIdenJoe – the physical and flexible stacking logics are the same with regards to firmware upgrades. We’ve tested staggered upgrades on MS425s in the past and they are not hitless. For that reason, staged upgrades across members of stacks aren’t supported.
Convergence of hardware forwarding information should occur within 30 seconds of a failure or in this case a reboot for upgrade, however, this period could be longer depending on the nature of the failure, the definition of full convergence, and the protocols involved. For instance, if it’s the active switch in the stack that fails, protocols such as OSPF will have to re-establish adjacencies and synchronize the database.
Technical Leader - Meraki Product Management: Switching / ccie 50782