In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Salaat (Prayer) has been ordained upon every believer a decree of specified time. The five daily prayers have their specified time, which every Muslim must observe. Timing system in the world also is not the same. Some have a longer time while others have a shorter time. When you therefore study in a Country that gives you an ample time to observe one prayer but denies you the other, such as having lectures during the prayer time, you are to observe the prayers that fall in the lecture free time. As for the Prayers that you have classes during their time, you should try your best to observe them during their time, because this is the basic principle for obligatory Prayers. You may ask permission or a time out which takes no more than five minutes.
If you are unable to gain this permission and you cannot perform them in their time, then you may combine the prayers according to the free time, such as with Dhur and ‘Asr; that is you can perform `Asr after finishing Dhur during Dhur time.
The same also applies to Maghrib. If you cannot gain a permission to perform it in time, you can combine it with `Isha; that is to perform it before `Isha’ during `Isha’ time.
And Allah knows best.