What are the mustahab times for performing all five salaah?

Fajr salaah should be offered when it is slightly bright and not when it is very dark.

In summer, one should not hasten towards reading Zuhr Salaah. It is mustahab to offer Zuhr Salaah after the intense heat rays elapse. In winter, it is preferable to offer Zuhr Salaah at the beginning of zuhr time.

Asr Salaah should be delayed till such a time that if after the entry of asr time one wishes to offer any nafl salaat, he can do so. However, one should not delay to such an extent that the sun turns yellow and its rays change in colour.

It is mustahab to offer the Maghrib Salaah immediately after sunset.

It is preferable that Esha Salaah be offered before one third of the night passes.

And Allah Ta'ala (الله تعالى) knows best.