Kolkata is 11.5 hours ahead of Denver

There is no standard 8-to-6 overlap. Someone joins early or late.

An 11.5-hour difference puts Denver and Kolkata out of sync — when one team is mid-morning, the other is fast asleep. Consider rotating the inconvenience: one week Denver takes the early call, the next week Kolkata does. Finally, Denver observes daylight saving and Kolkata doesn't, so this window shifts by an hour for part of the year — recheck it each spring and autumn.