280 hours, assuming an 8 hour day = 35 days / 7 weeks.
Did you mean 2800 hours max?
It looks like bad math all around. In ancient times (the previous millennium) companies would allow you to accumulate unlimited PTO at rates based on the years you worked at a company and when layoffs started to hit and they realized they had massive liabilities they demanded people take vacation until they were under a fairly modest limit until they realized a lot of their staff would be gone for more than a year (52 40 hour weeks is 2080 hours.)
The liability of the on the books thing is a myth. It's part of your compensation package and they know they can deny vacations enough that some people exceed the limit and simply lose the time. Even if you held on to your time until you quit they aren't paying any of your other benefits so it's still a corporate win in a cash out scenario. At every company I've ever worked for there was always a strong push for unpaid overtime which dwarfed any vacation and holiday pay so not only are they not really paying for those but they're collecting free work on top of it.
The only good strategy in this kind of environment is to leverage everything available to you to bulk your skills at your current company and jump for another 30%. To keep doing this the skills you gain must be both rare and valuable. I continue to be amazed how many people with STEM backgrounds don't understand how money is compounded, and having seen so many over 50 laid off over the past 40 years (longer than most careers) you really need to plan for an early retirement.