Hi,
For the VMI session logout timer, try this:
Go to SA>System>Authentication and under Cisco Unity PCA settings>Session Duration, change this value. This is a system-wide setting, so all users will be affected.
Keep in mind that the more active/logged in sessions at a time, the more potential (negative) impact to Unity's performance.
I've not seen ViewMail configured to play a prompt to PC when a new message is received-- the only thing I can think to ask you to try is to ensure that the message playback option is set to the local PC and not the phone.
I hope this helps.
