Vienna is 6 hours ahead of New York. Put the other way round: New York is 6 hours behind Vienna.
New York is UTC-4 in summer and UTC-5 in winter; Vienna is UTC+2 and UTC+1.
Working 09:00 to 17:00 in both cities leaves 2 hours in common: 09:00 to 11:00 in New York, which is 15:00 to 17:00 in Vienna. Those are the hours to aim a call at.
Both cities move their clocks for summer, and by the same hour, so the gap above holds for almost the whole year. It slips by an hour for the days between the two countries' switch dates, which do not line up exactly.
| New York | Vienna |
|---|---|
| 08:00 | 14:00 |
| 09:00 | 15:00 |
| 10:00 | 16:00 |
| 11:00 | 17:00 |
| 12:00 | 18:00 |
| 13:00 | 19:00 |
| 14:00 | 20:00 |
| 15:00 | 21:00 |
| 16:00 | 22:00 |
| 17:00 | 23:00 |
| 18:00 | 00:00 next day |
This page covers one pair. TimeGap takes a list: add every city you care about, drag one marker, and every row reads the same instant on its own clock. It marks the hours you would actually take a call, finds the window where the most people are reachable, flags public holidays, and puts the time you pick straight into Outlook or Google Calendar.