Each state, each county is different. Your husband's attorney should have clarified this for you at the time of the sentence. You should call the sheriff of the jail where your husband is and ask the sheriff if he will earn good time credit for an earlier release.
Most county jails in Alabama follow the rule that you get good time for every day served. As a general rule in Alabama, if he were forced to serve the entire sentence incarcerated, he would likely be released after around 6 months.