The explanation below was given by Dr. Rajab Abu Maleeh, on this issue:
“It should be known that it is not permissible to delay the prayer beyond its time because of work. Allah says,
“Men whom neither merchandise nor sale beguileth from remembrance of Allah and constancy in prayer and paying to the poor their due; who fear a day when hearts and eyeballs will be overturned; That Allah may reward them with the best of what they did, and increase reward for them of His bounty. Allah giveth blessings without stint to whom He will.” (Al-Nur, 37-38)
So you must organize your time at work in a way that will not interfere with your performing the prayers on time and work out an agreement on a suitable solution with the administration.
Secondly: If this is not possible, then it is permissible for you to join ‘Asr and Maghrib prayers before the start of your shift or afterwards. It should be noted that the prayers which are allowed to be joined according to shariah are Zuhr and ‘Asr, or Maghrib and ‘Isha’. These are the combinations mentioned in shariah. As for joining ‘Asr and Maghrib, this is not narrated in shariah and is not valid.
Thirdly: You must try hard to solve this problem. It will not take you more than ten minutes to do this thing, so you can agree with the boss that you will make up this time before or after your shift. In your country, there may be laws that protect the rights of minorities to practice their religion and which oblige bosses to respect the religion of those who work for them. You may have such laws which will enable you to ask for your rights.
If it is too difficult for you, and you cannot solve this problem with the administration, then you have to look for another job which will not conflict with your establishing regular prayer. If you cannot find any other job and you will be adversely affected by your leaving this job, then there is the hope that this may be regarded as a necessity that will permit your joining your prayers and there will be no sin on you in that case, in sha Allah.
You can join Zuhr and ‘Asr, at the time of either of them, and you can join Maghrib and ‘Isha’ at the time of either of them, depending on what is easier for you.
As for offering Prayer for people who have legal excuses, such as your case, they are required to seek medical treatment at first. Then, until they get recovered, there are two scholarly opinions in this regard. One of them is that those people should perform wudu‘ for each Salah and pray with that wudu‘ whatever they want of mandatory prayers till the time of the next prayer comes and they are not allowed to perform obligatory prayers while in the same state of Wudu‘. In other words, they have to observe wudu‘ one time again in order to perform extra obligatory prayers. The second opinion is that they are allowed to perform both mandatory and obligatory prayers as long as they are in the time of the obligatory prayer and in the same state of wudu’. That is to say, if they want to perform other obligatory prayers in the same time, they are permitted to do that without repeating wudu‘. However, the same opinions are applicable to making up for missed prayers.”