When you create your account, you'll be asked to choose your time zone and currency. You won't be able to change these settings after you choose them because they're used to determine how you're billed.Choosing your account time zone
Your reports, statistics, and billing are all affected by the time zone you select. For example, settings such as your daily budget run on a 24-hour schedule. We recommend you choose your local time zone so your budget cycle ends when your day ends.
In the event you set your account time zone in error, account time zones may be changed up to one time over the life of an account. To request such a change, please Request to change time zone
We can only reset your time zone once, so please choose your new time zone carefully. If your time zone has already been reset at your request, we will not be able to change it again.
Reference: Select Time Zone