Depends on what work they do.
Lots of self employed are very much tied to the work, have obligations to customers and other people, don't get paid if they don't work, and may even be contractually liable for losses if the don't finish a job on time etc.
Others will be far more flexible than an employee if their work involved flexible timescales, like freelancing/contracting, website design, graphic design, etc.
I've been running my own small accountancy practice for 25 years. At times, that means I'm very flexible as most work isn't time sensitive to within a few hours, I can usually slack off one day and pick up the work and catch up a day or two later. But, some days, I'll have appointments, or I'll have days working out at client premises, or specific deadlines on certain days of the month where I'm waiting for client data and then only have a small window of time to prepare and submit the return, etc. So, some days, I could easily just have a day off, or a lie in, etc., but others, I have to work, whatever else is thrown at me, as if I didn't I'm not only letting clients down, I could be on the hook for a late filing penalty!
Self employed aren't a homogenous mass all doing the same - different people, different types of work, different responsibilities.
That said, there are clearly "types" of people that use self employment merely as an excuse for not taking on their responsibilities and just using it as an excuse. I.e. maybe a tradie claiming to be too busy on a job, but still finding the time to go to the pub when he finished at 4 instead of picking up his child from school. Or an IT consultant claiming he's too busy to stay home and look after a poorly child, but finds time to spend the afternoon in the gym,