Following is how I might reply to a customer;  Release notes indicate the following regarding firmware updates; “A firmware update takes approximately 10 minutes per node.  Each node is updated individually, and is automatically restarted when the update is complete. “ This part is done in a rolling fashion so other than moving clients between nodes during the process it shouldn’t require an outage.  Keep in mind the SMB/CIFS session reset caveats that we’ve discussed.  As for the OneFS upgrade from 6.5 to 7.x, a good estimate is between 20 & 30 minutes total.  Remember that since this is a major upgrade, you'll be doing a simultaneous cluster restart so there will be a period of time where the cluster is unavailable to serve data.
I have a customer with an Isilon cluster made up of Qty 3 X200s and Qty 3 NL400s.  They are planning to do firmware updates and upgrade from OneFS 6.5 to 7.x. and they want an estimate of how long this will take.  What's a good estimate to give them?
How long will FW updates and a OneFS upgrade take?