Is work one of the excuses for which it is permissible to delay prayer beyond its time?
Question

I work at a time when it is not possible for me to offer Fajr and Zuhr prayers. It is permissible for me to offer them at a time after work is over?.
Praise be to Allah.It is not permissible for a Muslim to delay his prayers beyond the time when they are due without a legitimate excuse. Legitimate excuses which allow a Muslim to delay his prayers until the time for them is over include sleeping and forgetting. Doing worldly work is not an excuse for not praying or for delaying a prayer until its time is over. Rather one of the characteristics of the sincere believers is that they do not let business or trade distract them from remembering Allah and establishing regular prayer. 
Allah says (interpretation of the meaning): 
“In houses (mosques) which Allah has ordered to be raised (to be cleaned, and to be honoured), in them His Name is remembered [i.e. Adhan, Iqaamah, Salah (prayers), invocations, recitation of the Quran]. Therein glorify Him (Allah) in the mornings and in the afternoons or the evenings,
37. Men whom neither trade nor sale (business) diverts from the remembrance of Allah (with heart and tongue) nor from performing As-Salah (Iqaamat-as-Salah) nor from giving the Zakaah. They fear a Day when hearts and eyes will be overturned (out of the horror of the torment of the Day of Resurrection).
38. That Allah may reward them according to the best of their deeds, and add even more for them out of His Grace. And Allah provides without measure to whom He wills”
[al-Noor 24:36-38]
Even though these men engaged in trade, buying and selling, that was no excuse and it did not distract them from giving precedence to “the remembrance of Allah (with heart and tongue) nor from performing As-Salah (Iqaamat-as-Salah) nor from giving the Zakaah.”  Rather they made obedience to Allah and worship of Him their ultimate goal and purpose, and whatever came between them and that goal, they rejected it. 
Because giving up worldly interests is hard for most people, and earning and various kinds of trade are dear to them, and it is hard for them to give that up in most cases, and to give precedence to the rights of Allah, Allah mentions that which will motivate and encourage them, as He says: “They fear a Day when hearts and eyes will be overturned (out of the horror of the torment of the Day of Resurrection)” – because of the intensity of its horrors and suffering. Hence they will fear that Day, so it become easier for them to strive for the Hereafter and give up that which distracts them from it. 
Tafseer al-Sa’di. 
Concerning the obligation of offering prayers and the ruling on its timing, Allah says (interpretation of the meaning): 
“Verily, As-Salah (the prayer) is enjoined on the believers at fixed hours”
[al-Nisa’ 4:103].
Shaykh ‘Abd al-Rahmaan al-Sa’di said: 
This means it is enjoined at its time, which indicates that it is obligatory and that it has a time (to be offered) and is not valid at any other time. These are the times that are well known among the Muslims, young and old, scholars and ignorant. They learned that from their Prophet Muhammad (peace and blessings of Allah be upon him) who said: “Pray as you have seen me praying.” The phrase “on the believers” indicates that prayer is the measure of faith, and a the quality of person’s prayers corresponds with his level of faith. 
Tafseer al-Sa’di. 
And Allah says, warning those who delay their prayers until the time for them is over with no legitimate excuse (interpretation of the meaning): 
“Then, there has succeeded them a posterity who have given up As-Salaat (the prayers) [i.e. made their Salaat (prayers) to be lost, either by not offering them or by not offering them perfectly or by not offering them in their proper fixed times] and have followed lusts. So they will be thrown in Hell.
60. Except those who repent and believe (in the Oneness of Allah and His Messenger Muhammad), and work righteousness. Such will enter Paradise and they will not be wronged in aught”
[Maryam 19:59-60]
And Allah says (interpretation of the meaning): 
“So woe unto those performers of Salah (prayers) (hypocrites),
5. Those who delay their Salah (prayer from their stated fixed times)”
[Al-Maa’oon 107:4-5] 
Ibn Katheer said: 
It was narrated from Ibn Mas’ood that it was said to him that Allah mentions prayer a great deal in the Quran: “Those who delay their Salah (prayer from their stated fixed times)” [Al-Maa’oon 107:5] and “Those who remain constant in their Salah (prayers)” [al-Ma’aarij 70:23] and “and they are constant in guarding their Salah (prayers)” [al-An’aam 6:92]. Ibn Mas’ood said: (This means) offering prayers at the stated times. They said: We thought that these verses referred to not praying at all. He said: That is kufr. 
Al-Awzaa’i said, quoting from Ibraaheem ibn Yazeed, that ‘Umar ibn ‘Abd al-‘Azeez recited: “Then, there has succeeded them a posterity who have given up As-Salaat (the prayers) [i.e. made their Salaat (prayers) to be lost, either by not offering them or by not offering them perfectly or by not offering them in their proper fixed times] and have followed lusts. So they will be thrown in Hell” [Maryam 19:59]. Then he said: “Their giving up their prayers does not mean that they do not pray at all, rather it means that they have given up praying at the proper times.” 
Tafseer Ibn Katheer, 3/128, 129. 
So it is not permissible for you to delay your prayers from the proper time based on the excuse of work. If you cannot pray on time at work, then you should leave this job and look for another job which will not cause you to miss your prayers. The wise Muslim should not expose himself to the threat of his Lord and he should not sell his religious commitment for the sake of passing worldly interests. 
And Allah knows best.