Currently, three hours is typical. I used to run longer games, 5-7 hours, with occasional all-nighters. But I was much younger then, with far fewer responsibilities.
A few of my players and I did get away for a gaming weekend at a family cabin just before COVID-19 and got to play for ~18 hours over two days. Even then, though, we didn't run sessions for much longer than three hours—roughly three sessions per day with meals, hiking (well, snow-shoeing), and social time in between. (It was quite rewarding to get a session in right after breakfast!)