Explanation

Salat e Shukar is Mustahab

Mustahab means favored or virtuous actions

Mustahabb actions are those whose ruling in Islamic law falls between mubah and wajib

Salat e Shukar is also known as Sajdah Shukr

Shukr prayer (Prayer of thanks) is performed in order to thank Allah (swt) 

It doesn't have a specific time.

It is at least 2 rakahs.