On my days off I try to get household things done Early...like by 7 am. Then I can sew till about 11. Then, run any necessary errands, eat something and get back to sewing by 1-1:30, sew till hubby comes home around 4.
Sometimes I'mdoing prep work or hand stitching in my chair in the evening too.
So;
i don’t think there is any such thing as ( too long) as long as you take breaks and don’t over-tax your body.