Karachi is 11 hours ahead of Denver

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

The 11-hour offset between Denver and Karachi means there's no point hunting for a 9-to-5 overlap — there isn't one. Expect compromise: someone in Denver or Karachi will need to take the call outside the usual 9-to-5, so share that load. Finally, Denver observes daylight saving and Karachi doesn't, so this window shifts by an hour for part of the year — recheck it each spring and autumn.