The good conduct of any offender qualified for credit for preventive imprisonment pursuant to Article 29 of this Code, or of any convicted prisoner in any penal institution, rehabilitation or detention center or any other local jail shall entitle him to the following deductions from the period of his sentence:
1. During the first two years of imprisonment, he shall be allowed a deduction of twenty days for each month of good behavior during detention;
2. During the third to the fifth year, inclusive, of his imprisonment, he shall be allowed a reduction of twenty-three days for each month of good behavior during detention;
3. During the following years until the tenth year, inclusive, of his imprisonment, he shall be allowed a deduction of twenty-five days for each month of good behavior during detention;
4. During the eleventh and successive years of his imprisonment, he shall be allowed a deduction of thirty days for each month of good behavior during detention; and
5. At any time during the period of imprisonment, he shall be allowed another deduction of fifteen days, in addition to numbers one to four hereof, for each month of study, teaching or mentoring service time rendered.
An appeal by the accused shall not deprive him of entitlement to the above allowances for good conduct.