It’s *really* variable, and depends both on the pattern and on the person sewing.
For me (a slow sewist, limited time), it will almost always take me a couple of nights to make anything. Typically I’ll cut one night, sew the next night (or nights), and finish (hem, add buttons etc) on another night. So even for something super-quick to sew, I’m not churning out anything in a few hours.
That said, if I’m sewing something entirely on a serger, like cuffed PJ pants, or a long-sleeve knit shirt with cuffs and a band, I can knock it out in less than an hour. If I have to hem anything on my sewing machine, that adds another hour, minimum.
For me, sewing time increases with number of pattern pieces. Sleeves add extra time. Anything with buttons adds time. A simple shirt is probably faster to sew than simple pants, unless the pants don’t have pockets.
For O+S patterns, the ones that I have a chance at starting (from cutting) to finishing in a single session, which for me is never more than four hours, are the playtime leggings (especially if I cuff and add a waistband), FT raglan shirt, the School Bus tee, the Sailboat top (if I use snaps instead of buttons), Sunny Day shorts, and the sleepover PJ pants (if I omit the cuffs). I’ve only made one of the O+S dresses (rollerskate) – some of the others might also be quick to sew.
Others will have much different answers, though – I know I’m slow compared to many.
