How to bring down a application for certain period of time
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There is no direct support for something like this.
But, you could create a boolean constant you use to show/hide pages on a site, or other UI elements, to make that app non-/available to users.
where can we configure the constant
I am not sure what you want to know. I am talking about a constant in Appian.
docs.appian.com/.../Constants.html