No, I don't believe there is an actual release time for the tenants. You should be able to reach out to your Netskope rep and they should be able to give you a heads up the day of or before the update is scheduled. I will ask my rep today to see if there is a release page we can access.
So I was able to find a link that has up coming change notifications. https://support.netskope.com/hc/en-us/sections/200516187-Change-Notifications
This will provide info on up coming changes and not just the R98 release dates.
The admins of your account/tenant receive an email notification with all the upgrade schedule details. You can also check the Netskope Support site. Here's the R98 page (which was also shared above): https://support.netskope.com/hc/en-us/articles/5450892149143-Netskope-Upgrade-Release-98
You have to subscribe to the release note notices.
A link to the subscription instructions is on the first page of the release documentation but I'll provide the direct link to those instructions
Release Notes Subscription (netskope.com)
Or you can just shortcut the formal instructions and go to following page here in the community site, then click Options and Subscribe.
Netskope Community News