A call booked for 10:00 in Yokohama rings a Johannesburg desk at 03:00. Nobody picks up. The 7-hour gap between JST (UTC+9) and SAST (UTC+2) is fixed, so the mistake is easy to make and easy to fix once you see the pattern.
JST (UTC+9) vs SAST (UTC+2): a constant 7-hour difference
Yokohama runs on Japan Standard Time, always nine hours ahead of Coordinated Universal Time. Johannesburg uses South Africa Standard Time, always two hours ahead of UTC. Neither city observes daylight saving time, so the offset never shifts. Subtract seven hours from Yokohama time to get Johannesburg time. Add seven hours going the other way.
The gap holds on 15 January, 15 July, and every day in between. The only wobble comes when you compare Yokohama to a city that does change its clocks. Against Johannesburg, the maths stays put.
What is the best time for a Yokohama, Johannesburg call?
The shared window inside a standard workday is tight. Johannesburg business hours typically run 08:00 to 17:00. That is 15:00 to 00:00 in Yokohama. The overlap sits entirely in Yokohama’s late afternoon and evening.
| Yokohama time (JST) | Johannesburg time (SAST) |
|---|---|
| 08:00 | 01:00 |
| 09:00 | 02:00 |
| 10:00 | 03:00 |
| 11:00 | 04:00 |
| 12:00 | 05:00 |
| 13:00 | 06:00 |
| 14:00 | 07:00 |
| 15:00 | 08:00 |
| 16:00 | 09:00 |
| 17:00 | 10:00 |
| 18:00 | 11:00 |
| 19:00 | 12:00 |
| 20:00 | 13:00 |
| 21:00 | 14:00 |
| 22:00 | 15:00 |
| 23:00 | 16:00 |
| 00:00 | 17:00 |
The strongest slot for a live conversation is 15:00 to 18:00 Yokohama time, which is 08:00 to 11:00 in Johannesburg. That catches the start of the South African workday and the tail end of the Japanese one.
When the Yokohama, Johannesburg overlap advice fails
Aiming for the overlap is the default rule, and for most people that means Yokohama’s late afternoon. But the standard window still misses two groups.
First, shift workers. A Johannesburg contact who starts at 06:00 needs you at 13:00 Yokohama time, when most Japanese offices are still in their post-lunch rhythm. That works only if the Yokohama side can break away early in the afternoon.
Second, early birds in Yokohama. Starting at 07:00 puts you at midnight Johannesburg time. The only fix is to push the call to your own lunch break, around 12:00 Yokohama time, which is 05:00 in Johannesburg. That demands a Johannesburg party willing to start unusually early.
For the full picture of each city’s working hours, see the Yokohama business hours guide and the best times to call Yokohama from any location.