Thanks for your feature request! Managing time zones is always a challenge for any software.
First, I wanted to mention that you can set emails to be sent at a specific time in the contact's time zone in Campaigns. The Wait element right before the Send Email element includes a drop down to specify the timezone.
Timing for things like broadcast emails, timers on pages, etc. do use the time zone of the computer they are logging in from; displays of date and time people opted in, purchased products, and the like are also converted to the viewer's time zone. That is the default used by programs like Google Calendar for events, so we're not unusual in that regard.
We'll keep this open to see if people want to have a setting for a global date and time zone to be used for all users logging into the account.
