Set Timout for VPN Session

[verpfsense]

Hello Guys

We are using OpenVPN with FreeRadius and Google Authenticator.
Where can i set the time for a session timeout if the connection is lost from the client?

Users are sometimes connected over mobile in the train with a bit of an unstable connection, so they loose the internet for 2 minutes. So i want the client to be able to reconnect without entering the credentials again if the timeout is shorter than lets say 5 minutes.

Thanks for your help.