If you want to change timezone for a single account on a cPanel server you can follow following simple steps for this.
1) Login to the server as root.
2) Navigate to the home directory of the account and create a .htaccess file. If it already exists you can add the following line to the top of the file.
3) Insert the following line in it
Replace the TimeZone with appropriate time zone as per your convenience. For Eg:: Asia/CalcuttaSetEnv TZ “TimeZone”
php_value date.timezone “TimeZone”
Refer PHP: List of Supported Timezones - Manual for the list of available timezones.
You are done.