I’m seeing IST in my zonefile:
# zdump /usr/share/zoneinfo/Asia/Kolkata
/usr/share/zoneinfo/Asia/Kolkata Wed Oct 24 20:44:26 2018 IST
Another interesting tidbit is that I’m seeing Calcutta there too:
# zdump /usr/share/zoneinfo/Asia/Calcutta
/usr/share/zoneinfo/Asia/Calcutta Wed Oct 24 20:45:54 2018 IST
Can you try putting a info.php file with this code:
Then open the script from your website (ex: http://example.com/info.php) and see what timezone is showing there. I’m suspecting something else is overwriting your timezone. Perhaps in another ini file. Seach for php.ini on the page as that will show you where the default.timezone is being sourced from.