In this context, date of agreed resignation is the last working day.
When you hand out notice, you are informing about the upcoming resignation, and your last working day is when you actually resign and end official relation with your employeer.
Money talks. You can't convince them to lower rent, only the market can do that. You must have a credible plan to move to less costly office space, or to drop your office space entirely and work remotely.
Only then can you negotiate from a position of strength.
In other words you need a credible Best Alternative To a Negotiated Agreement (BATNA). Look up ...
But I don't want to stay that long, how to deal with this situation?
Upper management wants everyone to work more than 44 hours per week.
Your contract requires 44 hours.
You usually work 40-42 hours
You don't want to stay longer
Clearly, this is a mismatch between what you want in your work situation and what upper management demands.
Thus, you should ...
You should really, really tell us where you are located.
The contract means that you will be unemployed for at least one month. In many locations, such a contract will be void. On the other hand, even if void, you may have to fight about it in court.
The next time you sign a contract, read it before signing, and strike out any terms like these. (I think ...
If you want to make a point in educating higher management, either approach is risky, as they probably believe in what they teach and opposing it - in their eyes - means willfully hurting the company's productivity.
Still, if you want to do something, rather make sure to have the backing of as many colleagues as possible. Then do something together, e.g. ...