Confederate States of America

Probably several decades, like 50 -60 years, maybe even longer.
Automated machinery was improving steadily and the cost of using machines in cotton production became cheaper than using slaves in the 1900s.
By 1890s, slaves would largely be used for domestic chores and in factories rather than hard labour in the field. The Americans would still preserve slavery for some time to exploit the cheap labours.
By 1910s, slavery would've been abolished or relaxed due to World war I. Many Black men would be freed in exchange for their service in the military.
By 1930s the economic depression would be another great opportunity to call for the end of slavery system in CSA with all the social chaos going on. The ensuing World war 2 would deal a final blow to the slavery system as colonial empires crumble and slavery deemed highly intolerable worldwide in the new era.
Civil Rights Movement would be delayed and desegregation may only be officially implemented in the 1980s or even 1990s. The first Black President of the Confederate States of America would've been elected at a much later time in the 2020s or 2030s.