Optimal value of hearbeatInterval

We want to know what is the least value for heartbeatInterval for Vaadin 7 applications.

Since we are using this to clean-up unused UI instances (for exampled created because of refresh browser since we do not preserve the states), we want to keep this value as minimum as possible without any performance overhead.

The default value seems to be 5 min x 3 times = 15 min before the DetachEvent is sent to the UI application which seems too long for us.

Please advise.

There is nobody to respond this?