Yes, as long as the clients have been set up with individual user accounts, you can set the time individually for each of those clients.
1. To adjust the time on a user account select the downward arrow next to the name displayed in the top right hand corner of the dashboard as shown in the following image.
2. Then select Timezone.
3. The following window will appear. Select the appropriate country from the dropdown menu.
4. Then select the 'Apply' button for that timezone to be applied to that individual user account.