Assembly: System.Web.Extensions (in System.Web.Extensions.dll)
The Visible property is overridden in the Timer class to prevent setting this property. The Visible property returns true if the client component of the Timer class is included in the Web page, even if Enabled is set to false. The Visible property returns false when it is inside a container, such as an UpdatePanel control, whose Visible property is set to false.
Available since 3.5