Hour of the First Watch and Supererogaty Prayers

[ibelieveinitonly]

As Salaam Alaikum,
I am reading the Quran right now I came across these verses

1778-81
Observe the service of prayer from the sun's declining from the meridian to the darkening of the night, and the recitation at dawn. Indeed the Recitation at dawn is palpably evident. Say a supererogatory prayer at the hour of the first watch Your Lord may raise you to a most exalted station. And pray "O my Lord, let my entry be with honour, and let my exit be with honour, and grant me power from You which would help me." And say "Truth has come and falsehood nullified." Verily falsehood is perishable.

My questionare

1.) What is the hour of the first watch?
2.) When do we say these prayers? During salat? After salat? SHould these prayers be included in the salat?

Thanks