There are two timezones in the Mursion Portal: the User Timezone and the Calendar Timezone.
The User Timezone is the primary, default timezone for all of your Portal activity. Notifications from the Portal, including Session confirmation and reminder emails reference the User Timezone. This is set during your account creation, and can also be adjusted at any time by clicking the User Profile button in the top-right corner of the Portal, clicking "My Profile", and selecting your desired time zone.
The Calendar Timezone, found in the Calendar tab of the Mursion Portal, is your view of the schedule based on your computer's (or other device's) current timezone, regardless of your profile timezone.
You may adjust this at any time, which will change the time zones for all sessions displayed by the Calendar view.
Note that the Calendar Timezone is a tool that only applies to how you view sessions in the calendar; your confirmation e-mails will still reference your User Timezone.