Virtue of Praying 4 Rak`ahs before and After Dhuhr
Question

I read in a religious publication that whoever prays four Rak`ahs before Dhuhr prayer and four Rak`ahs after it, Allah will ransom him from the Fire on the Day of Resurrection. If this is true, when should I pray the Sunnah of Dhuhr prayer?
Praise be to Allah.Virtue of praying 4 Rak`ahs before and after Dhuhr
It is recommended to pray four Rak`ahs before Dhuhr prayer and four after it. An-Nasa’i (1817) and At-Tirmidhi (428) narrated from Umm Habibah (may Allah be pleased with her) that the Prophet (peace and blessings of Allah be upon him) said: “Whoever prays four (Rak`ahs) before Dhuhr and four after it, the Fire will not touch him.” 
The version narrated by At-Tirmidhi (may Allah have mercy on him) says: “Whoever regularly performs four Rak`ahs before Dhuhr and four after it, Allah will forbid him to the Fire.” (Classed as authentic by Al-Albani in Sahih An-Nasa’i)
These Rak`ahs are not something different from the regular Sunnah (Sunnah Ratibah) of Dhuhr prayer, rather they are the regular Sunnah. 
But what is certain and should not be abandoned under any circumstances is praying four Rak`ahs before Dhuhr and two Rak`ahs after it. As for doing four Rak`ahs after it, if a person does that following this Hadith, then he has done the Sunnah and Allah will reward him, but if he limits it to two Rak`ahs, that is sufficient.  
Time for offering Sunnah for Dhuhr
The time for offering the Sunnah prayer before Dhuhr is between the Adhan of Dhuhr and the obligatory prayer. 
The time for offering the Sunnah prayer after Dhuhr is from after Dhuhr prayer until the Adhan of `Asr. 
For more details, please see the following answers: 33779 , 1048 , 12844 , and 181043 .
And Allah knows best.