The catch-all statement seems pretty clear -- they own it (unless you dispute it in a court of law -- but who will invest in your thing in the meantime ?).

Now, perhaps they are benevolent and are willing to allow you do your thing in the spare time. But, if you really think there is money to be made, spend some money on actual legal advice.

Btw, if I were your boss and would read this message I would be kinda conflictual about granting you an exception from the contract for another reason: you seem to over-work yourself. Now, when you hire somebody for a full-time job you assume a given productivity. If the person is spending another 6-8 hours a day doing his side project until he's about to collapse -- how much productivity is the company losing ? Just another angle to look at it.