In the log-in screen for Webmail, you will notice a choice of security options:
Public or shared computer
Use this option if you are viewing your Webmail on lab or shared computers. It has a 60 minute timeout session so that if you leave the computer, your email session will quickly automatically terminate and not be left open to others.
Use this option if you are using Webmail from your personal or home computer. This option has a 90 minute timeout so that you’re less likely to lose an email you started when you step away from your computer (e.g., if the telephone rings or you need a coffee break!)