It costs you nothing, takes very little time, and is entirely feasible. Therefore, whenever you are able to secure a moment during your studies to perform each prayer within its appointed time, doing so is a binding duty.

If, however, you have tried to obtain such an opportunity but have been unable to, and if the studies themselves are essential so that abandoning them would harm you, then I see no objection to combining two prayers in the manner mentioned in your question: performing ʿAṣr together with Ẓuhr as an early combination (jamʿ taqdīm) and performing Maghrib together with ʿIshāʾ as a delayed combination (jamʿ taʾkhīr). This falls under the excuses that permit combining, for the jurists have stated that one of the valid excuses is when a person would suffer harm by giving up a livelihood he needs. Accordingly, if giving up your studies would harm you and you have not been granted time by the authorities to pray during working hours, then—in my view—combining the prayers in this situation is permissible.

What is not permissible, however, is to perform the prayers later as make-ups (qaḍāʾ), as was also mentioned in the question. Allah knows best.

Question: Is it permissible to combine the prayers without a valid excuse, and what is the authenticity of the ḥadīth stating that the Messenger of Allah combined the prayers when there was neither fear nor illness? Please enlighten me about this, and may Allah bless you.

Answer: Combining the prayers without an excuse is impermissible, and the prayer is not valid in that case, for it would be offered outside its prescribed time without a Sharʿī excuse. Allah the Exalted says, “Indeed, the prayer is enjoined upon the believers at fixed times” (Sūrat al-Nisāʾ 4:103). Combining is only