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.
These are the paths to get to each CCX logs through CLI. They may be helpful if you are having issues accessing RTMT or downloading logs through it.
If you want to download them you have to prefix "file get " and you can add one of the options (re...