How To Write A Formal Letter Asking For Release From Employer To Do Further Studies?

I would like to seek your permission to appear for my 1st semester examination (3-Papers of 3 hours daily) which is scheduled to be held from 7th, 9th and on 15th of June. During this short period, I'll be able to attend office from 11:30am instead of 9:30am as my exam time is from 9 to 11 o'clock in the morning. However, after examinations are over - I'll work overtime to adjust my absence time so as to not have any 'late coming' salary deductions.
Thank you for your cooperation