What time zone does Chargebee follow for updating reports?

This article also answers:

Is it possible to change the timezone of my site?

All the reports across your site will follow the time zone in your Chargebee site. You can find more details about time zones in here.

To change the time zone in your Chargebee site just go to Settings >> Business Profile (under Billing section) and hit Change time zone. Here, you also have the option to enable UTC time zone for your data exports. Please refer screenshot below.