The options at the county jail level are significantly more limited than what you find in state or federal prison, and Meade County is no exception.
County jails are designed for short-term housing. The programming infrastructure that exists in longer-term facilities, vocational training, substance abuse treatment, college courses, and similar offerings, simply does not exist at most county jails because the population turns over too quickly to justify building it out. The GED program is typically the most substantive educational offering available, and not every county jail even has that.
In terms of actually cutting time, the mechanisms are limited at the county level. Early release at Meade County Detention Center has historically been tied to overcrowding rather than program completion. When the facility gets too full, lower-risk inmates may be released early to manage population, but that is an administrative decision made by the facility rather than something an inmate can earn through coursework.
If your nephew is facing a longer sentence that will eventually move him to a state facility, that is where the real programming opportunities open up. State and federal institutions have robust educational and vocational offerings specifically because the sentences are long enough to make completion meaningful, and in some cases those programs carry genuine sentence reduction benefits.
For now, encourage him to pursue the GED if he has not already completed it. It is the most substantive thing available at his level and it carries real value on the outside regardless of whether it affects his release date.