Not a lot. The crew day is heavily constrained and the astronauts have a never-ending list of tasks to do. The crew gets one and a half hours every morning after they wake up to eat breakfast and do anything else they can fit in that time. They get 1 hour for lunch and then 2 hours at the end of the day after the evening conference with Mission Control. After that, they get eight and a half hours for sleep. They do get weekends and holidays off.
So in total, they only get 4.5 hours per day to eat meals and do something relaxing.
Occasionally, crew will need to work on a weekend either to support an ISS visiting vehicle or some other critical operation and when they do, we'll give them an off-day at the next opportunity.
You can find ISS mission timelines for each day here: NASA - International Space Station Timelines
You can also follow along for a given day's activities here: ISS live!
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