بِسْمِ اللهِ الرَّحْمنِ الرَّحِيمِ
The Messenger of Allah (صلى الله عليه وسلم) used to perform four Rak'ah prayer after the declining of the sun before Zuhr prayer and would say " This is an hour at which the gates of heaven are opened and I like that my good deeds should rise to heaven at that time."
Note: The prophet (صلى الله عليه وسلم) used to perform the four Rak'ah Sunnah of the Zuhr prayer when the sun started declining. In fact except for Isha he would perform every salat at its early hours.
Zuhr has 12 Rak'ats
Would you not like your good deeds to rise to heaven when the gates open?