On the one hand, I don't want to ruin the weekend for students who may be working on my assignment at the last minute.
Leaving the assignment at the last minute, especially in order to enjoy the weekend, sounds more like a choice than an obligation. I don't think it's your responsibility to do time and goal management for your students, especially if they are adults.
Otherwise I want to agree with Solar Mike, just pick something and stick to it. Your student will manage their time to make things work for them.