• The user’s timezone
• US Pacific Timezone
• US Eastern timezone
• The advertiser’s timezone

The correct answer is: The advertiser’s timezone

Explanation: In-Display & Video 360, the time zone of your advertiser affects the start/end dates for line items and insertion orders, and the time windows used for counting impressions, clicks, and conversions.
Read more here: https://support.google.com/displayvideo/answer/3184282