The correct opinion is that you can pray Tahiyyat al-Masjid at all times, even after Fajr and after ‘Asr because of the general applicability of the hadith “When any one of you enters the Mosque, he should not sit down until he has prayed two rak`ahs.”

Salat Al-Awwabin is known as Salat Ad-Duha, and may consist of 2, 4, 6 or 8 Rak`ahs. It should be prayed after the sun has risen and before the time for Dhuhr approaches.

The confirmed sunnah prayers are: 1- 4 rak’ahs before Zhuhr; 2- 2 rak’ahs after Zhuhr; 3- 2 rak’ahs after Maghrib; 4- 2 rak’ahs after ‘Isha; and 5- 2 rak’ahs before the Fajr.