Kolkata and Delhi are in the same time zone. Both cities use Indian Standard Time (IST, UTC+5:30). When it's noon in Kolkata, it's also noon in Delhi.
India uses a single time zone across the entire country.
Any time works! Since both cities are in the same time zone, scheduling is never an issue.
Kolkata and Delhi are two of India's major metropolitan cities. Flights connect them in about 2 hours, while the Rajdhani Express train takes about 17 hours.