I can spend a solid hour in the sun before I start to burn, assuming I have a hat on my head.

I've also noticed some correlation between my diet and how fast I burn. Whenever my metabolism is running at/near ketogenesis, it seems like it takes a lot longer for the sun to affect me.

Yes, some stuff make your skin more sensitive to light than others. For example, you should avoid vitamin A creams and some herbs during summer because they increase risk of permanent skin discoloration.

I experienced similar reaction when i was doing keto. It became far more difficult to burn that summer

Just so you know, burning & cancer isn't the only reason to avoid strong sunlight - it also causes skin aging (i.e. wrinkles). If you don't want to be super wrinkly when you're old, wear suncream!