The Fardh - obligatory rakats of Dhuhr is 4 and a total of 12 rakats: 4 sunnat, 4 fard, 2 sunnat, 2 nafl
The Dhuhr prayer is one of the five mandatory salah (Islamic prayer). Dhuhr prayer is a four rakah prayer. There are a few optional prayers.
The first four rakat is sunnah muakkadah, so some people do not pray it and begin with the 4 fard. After four rakat fard, two rakat sunnah muakkadah and two rakat nafl
Fardh - obligatory someone who ignores Fardh intentionally, knowing that it is an obligation, becomes a kaafir (disbeliever) (that is the opinion of most scholars)
Sunnat muakkadah - those actions of Hazrat Muhammad (ﺻﻠﯽ الله ﺗﻌﺎﻟﯽٰ ﻋﻠﯿﮧ ﻭﺍٓﻟﮧ ﻭﺳﻠﻢ) (peace be upon him) that were done regularly. someone who leaves it out due to a valid reason will not be sinning but who doesn t have a valid reason will be sinning.
Nafl - optional.
Time: The time for Dhuhr prayer is at after the sun passes its zenith and lasts until 20 min (approx) and before the call for the Asr prayer is to be given.
There is a hadith which says; “During the Dhuhr Salat’s time, the gates of heaven get opened.”
And Allah knows best