By function and design, enslaved people existing in a system of chattel slavery had no say over how they spent their time. This isn't to say every minute of every day was scheduled by their owner, but rather, how they spent their time not doing labor was shaped by their enslavers and the rules and systems around them.
/u/sowser has answered a few previous questions that address what you're asking and are worth reading to get a better understanding of an enslaved person's lived experiences.
Sowser's answer touches upon it but I want to go farther into education. In most places during the antebellum period, white lawmakers passed laws and policies that allowed them to punish enslaved people who were found to be engaged in literacy activities. In some cases, the laws stated that an enslaved person caught with books or paper could be whipped by the person who found the illegal literacy materials, even if the person wasn't their enslaver. This meant, in order to protect valuable property, enslavers and their employees would routinely search enslaved people's sleeping and private spaces to ensure there were no illicit materials. The constant stress of surveillance inevitably had a negative impact on enslaved people during their non-work time. In other states, anti-literacy laws extended to white abolitionists and free Black adults who worked to support literacy efforts among enslaved adults and children.
That said, enslaved people were full human beings, with their own hopes, aspirations, dreams, and wonderings. This meant that, despite the threat of corporal punishment, it was not uncommon for an enslaved person to use time not engaged in work tasks to try and acquire the ability to read and write English (there are records, including first person anecdotes, of enslaved people arriving in America with the ability to read and write Arabic.) There were multiple reasons for trying to acquire literacy skills - for some, it was about organizing uprisings, others it was to read religious texts independent of someone's interpretation, and for many, it was a matter of claiming their basic humanity or working to give their children something they didn't have. These same reasons were cited by the white lawmakers working to pass the laws. Skills seen as essential for liberation to the enslaved person were seen as a threat by their enslaver.
Living under these laws as a person with some degree of agency, every enslaved person had to make an informed decision around the risks related to learning to read, or teaching someone else. So, in effect, part of their non-work time was spent trying to figure out how get around the rules and systems set in place by their owner. For others, non-work time, especially before dawn, involved meeting in secret schools run by free Black adults and white abolitionists.