Are the Sunnah prayers that precede a Fard prayer to be performed before the prayer's time begins, or after it, or before the Iqamah for the prayer?

The regular Sunan (supererogatory prayers) are of two types: pre-Fard (two rak'ahs before Fajr and four before Dhuhr), and post-Fard (two rak'ahs after Dhuhr, two rak'ahs after Maghrib, and two rak'ahs after Ishaa). Their virtue is the building of a house in Paradise for whoever prays them, based on the saying of the Prophet, peace and blessings be upon him: "Whoever prays twelve rak'ahs in a day and night, a house will be built for him in Paradise: four rak'ahs before Dhuhr, two after it, two after Maghrib, two after Ishaa, and two before Fajr prayer." The time for the pre-Fard Sunnah is from the beginning of the prayer's time until its establishment (Iqamah), and for the post-Fard Sunnah, it is from after the salutation of the obligatory prayer until its time expires. The pre-Fard Sunnah is not valid before the prayer's time begins.