Hi Ai Okabe,
You can set the time zone for each instance by going to Settings > Profile > Time Zone.
This changes the displayed time zone for your eloqua instance. Although the data in Eloqua still refers to EST time zone.
For example, once you change the time zone of your instance, the form data will be displayed in your chosen time zone but when you import the same data it will still be pulled in EST time zone.
Hope this helps.
Ankit