The time stamps reflected on the Samsara Cloud Dashboard are based on the timezone of the computer/device you are viewing the site on, with the exception of Driver's Hours of Service logs.
Hours of Service logs are based on the Home Terminal Timezone as configured under Settings > Drivers for that particular driver on the Dashboard. Drivers should be advised to configure their mobile device to automatically set date and time.
How to Set Organization Timezone:
In order to set your Organization Timezone, you will go to Settings > General > Language and Region > Timezone.
How to Set Home Terminal Timezone for Drivers:
In order to set Home Terminal Timezone for Drivers, you will go to Settings > Drivers > Edit.
Scroll down to Home Terminal Time Zone to select the proper time zone.