London is 5 hours ahead of Montréal. Put the other way round: Montréal is 5 hours behind London.
Montréal is UTC-4 in summer and UTC-5 in winter; London is UTC+1 and UTC.
Working 09:00 to 17:00 in both cities leaves 3 hours in common: 09:00 to 12:00 in Montréal, which is 14:00 to 17:00 in London. 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.
| Montréal | London |
|---|---|
| 08:00 | 13:00 |
| 09:00 | 14:00 |
| 10:00 | 15:00 |
| 11:00 | 16:00 |
| 12:00 | 17:00 |
| 13:00 | 18:00 |
| 14:00 | 19:00 |
| 15:00 | 20:00 |
| 16:00 | 21:00 |
| 17:00 | 22:00 |
| 18:00 | 23:00 |
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.