Time to update vnx5200 software and latency of datamover failover

I want to plan and upgrade to our VNX5200 with USM and need to accordingly have time set aside for this.  How long does this type of update typically take (not counting the software download as I am downloading them with USM to C:\emc\repository\Downloads\VNX beforehand)?

We will be going from

VNX for File: 8.1.2-51 to 8.1.8.119

VNX for Block: 05.33.000.5.052 to 05.33.008.5.119

6 hosts are connected via 10gbps jumbo frame Ethernet using NFS to run vmware virtual machines to this array.

Need to know when the datamovers fail over, what type of latency will the VM's see to their datastores?  I know this will create SCSI timeout logs in the event logs for Windows VM's, but if the latency is short enough they should be able to recover, or just run with the same type of reduced performance when Veeam is completing a backup job (snapshot consolidation).  I'm looking for a figure, is it 100ms, 250ms, 500ms, or more?  I think anything more than 250ms would be noticeable by the VM.