Being job cautious !!

It depends on the job pressure you are exposed to. In case, you are one of the key persons handling the job related to your company and if there is no proper back up for you, when you go on leave for your exams, it could lead to additional pressure on you, where in the management may call you during your study leave period to fix any issue that was not adeptly handled or was facing difficulties without your support. 

When there is complete support for going on leave without disturbance, then you would be more relaxed and think only about passing your exams. Thus, at the end of the day, it is possible to manage passing your exams, provided your plans are well executed and you get equal support from your employer.