Day extension or no?

I give my students 24 hours after the deadline to add annotations/replies. So far, it has not resulted in any problems. I know that Sheila worried students might abuse such a window, and be working on their assignment during class, but I think I've solved that problem by making the deadline a couple hours before class begins. The drop-off in terms of points they can earn after the deadline seems to be pretty steep, so if they don't get in and do the work right away (i.e., in the first couple hours), it is not worth their time.