If he was given four years suspended sentence, THAT is his "good time". He is only doing 20% of his sentence. The posted release date of July is probably correct.
https://www.inmateaid.com/ask-the-inmate/my-brother-was-sentenced-to-5-years-suspended-to-4-he-has-served-a-year-which-he-was-given-credit-for-he-was-told-that-his-release-date-is-in-july-does-it-include-good-time-or-no#answer
Accepted Answer Date Created: March 02,2018