The answer to the question "How much more quickly does night come on Mars compared to Earth? Will it be easier to see Mercury there?" says Martian twilight can last up to two hours.
Has any lander studied how bright the Martian landscape generally gets during any time of twilight? Is there a way of comparing the Martian landscape brightness to the brightness of the different phases of the moon on a cloudless night on Earth? Graph below is in foot-candles.