Yes 6 hours is on the extreme end. It is not a daily occurrence. IMHO, the problem is what typically should be a long term project is due in a short duration of time (days not weeks) . And those extreme man hours on the weekend were allocated to the same projects to prevent procrastination. It seems like 1 teacher is going pretty extreme with her expectations. The rest seem to have the normal expectations of their students.
Just curious. At what age/grade is it appropriate for any student to deal with short timeframe project/assignment? Based on your description, having weeks instead of days is what you're calling "unreasonable expectations"? (along with the work the goes with that)
Typically, what I've seen (3 kids) over the years is that so called multi weeks projects are waste of time as NO kids starts them early. Most often, there is a spike of activities about a week (or day or two before...) before its due. In some instances, the teacher has kids work on the project components during the weeks leading up to submittal. In other words, no one element is beyond reasonableness.
My sense is, after reading few of your replies herein, that this is the first teacher your kid has had that increased expectations in a step, rather than a gradual increase of workload. Also, isn't dealing with this sort of change part of growing up in an educational context?
In any case, this particular problem sounds temporary, as you've indicated that its one teacher, so your issue is much more focused and is about getting through this semester. For that, I recommend doing nothing different and learn to get through it. If it happens again, the next time, your kid will be much more able to handle it having gone through it now.