All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
The prayer is the most significant matter in the life of a Muslim. Preserving it and performing it as it should be is among the great obligations. Allaah commands and encourages observing prayer in many verses of the Quran and the Prophet also did as reported in many narrations. These rulings are well-known to every Muslim.
Allaah has fixed a specific time for each prayer and the Prophet stated its details. Allaah orders the believers to observe the prayers in their fixed times. Allaah Says (which means): {Indeed, prayer has been decreed upon the believers a decree of specified times.}[Quran 4:103]. Therefore, performing prayer before its prescribed specific time or delaying it from that time is forbidden except in times or under certain circumstances specified in Islam.
The reason mentioned by the questioner that the starting time of the night prayer is too late while the starting time of the dawn prayer is too early, is not a religiously valid reason to perform the night prayer before its prescribed specified time or the dawn prayer after its specified time. It is compulsory to perform them both in their prescribed times. Delaying the dawn prayer until after the sunrise intentionally is among the great major sins which necessitates repentance. If the time of the night prayer is at eleven o'clock and the time of the dawn prayer is at five o'clock, as you mentioned, then the period between them is five hours which is sufficient for relaxation and sleeping. Many practicing Muslims in the West who abide by their religious duties perform the prayers in their specified times even if the time of the night prayer starts late and the time of the dawn prayer starts early.
A Muslim should fear Allaah, be steadfast on his religion and should not seek excuses to neglect his religious duties. If a person can not avoid work for his worldly life then how he could give up working for his next life which is more important than this life.
Prophetic narrations contain many virtues exclusively for the dawn prayer; for example the Prophet said: "Whoever prays the two cool prayers ('Asr and Fajr) will be admitted to
Though many good predecessors disliked sleeping after the dawn prayer, if one feels tired especially if he went to sleep late or has no work to do, then there is no harm, Allaah willing, in sleeping after the dawn prayer. This is better than neglecting the dawn prayer or delaying it from its prescribed time.
Allaah Knows best.