Update Dialog Instance option in High Availability system Upgrade

Dear Experts,

I have completed my sap upgrade from EHP4 to EHP7 in Dev and QAS system.

Now i want to perform upgrade in my production system.

Here my doubt is production system is HA system i.e. i have one central instance, one database instance and 5 application servers.

So in SUM tool while doing high availability system upgrade we have one option Update Dialog Instance in configuration phase.

So if i select that option, My downtime will increase or it will be same as in Qas and Dev.

If i wont select that option what will happen.

Expecting helpful reply.

Please suggest.

Regards,

Karthik Kanagala