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The deadline is part of the assignments.  When the teacher grades them is irrelevant.
stop being lazy

Lol do you have any idea of the workload a teacher has?  Or that grading is usually done outside of work hours (and is thus unpaid work)?
If you turn your work in late, that’s even later that the teacher is able to grade it and hand it back.  Get your work done and turned in. >

I will admit I had some teacher who were lazy and took forever, but I also knew some who would stay up late to make sure work was graded in a fair manner and time frame >

I don’t think you understand how school works…
Teachers and students are not equal.
The student deadlines do matter and exist in school to keep your curriculum paced evenly and try to keep things fair between students. It would be chaos if every student was turning in different lessons at different times. 
But the teachers “grading deadlines” they set for themselves. Those can be flexible and I don’t remember any hard deadlines for those. Those are more like soft guidelines. 
You have 6 teachers for 6 classes…. They have 100+ students…so yeah it’s going to take longer for them to grade ALL the assignments then it took you to make it. 
On top of that, they have hours of lesson planning, school meetings, administrative work, mandatory further education hours, ect. The average teacher is not lazy. >

I think teachers have to hand in all grades by the end of the school year