How long after sunset can Maghrib salaah be performed?

Maghrib Salaah should ideally be performed as soon as the sun has set.

However, the time for Maghrib Salaah lasts until the (white) twilight remains in the sky. (Shaami 1/361)

In South Africa this is approximately an hour and twenty minutes to one and a half hours after sunset, depending on the time of year. These times vary depending on the season.

Salaah times for many cities in Southern Africa may be accessed from the link below:

Perpetual Salaah Times (jamiat.org.za)

And Allah Ta’ala Knows Best