Timezone overlap calculator.
and
Assuming a 9:00 to 18:00 working day in each place, the result above is the window when both teams are at their desks. Two to four shared hours is workable for standups and reviews; under two means one side flexes or the work goes fully asynchronous.
Making a thin overlap work
Teams that run well on small overlaps do three things: they spend the shared hours on decisions rather than status (status lives in writing), they keep one live picture of who is actually working so nobody pings at 2am to check, and they judge output over presence. The middle one is our day job: TimeNova shows an offshore or remote team's real day, in everyone's own timezone, with hours both sides can trust. See time tracking for offshore teams.