Your account time zone serves as the default time zone for your campaigns. If you change your account time zone, the time zone for all campaigns will automatically switch to your new time zone.
Keep in mind that there are several, wide-ranging impacts when you change your time zone.
For example: You changed your account time zone on August 1, 2017. The performance data prior to August 2017 will reference the old time zone. All performance data from August 1, 2017, and onwards will reference the new time zone. That distinction may be important if you want to analyze hour-by-hour performance.
Immediately after you update your account time zone, you may see some hours with no data and some hours with double the amount of usual data. Please allow 1-2 days for reporting to settle in the new time zone.
For example, if you change your account time zone from Eastern Time to Pacific Time, you'll gain three hours to that day because of the time difference. Those three extra hours may lead to more performance and to extra spend as well. We strongly encourage you to monitor performance and to wait for a couple of days for your reporting to settle in the new time zone before you optimize your campaigns.