Also when do I eat it?
I ate my scarlettes when they were red, heavy, chunky, juicy and big.
For black varieties, it should be totally black, I guess...
I was tempted to wait till it fell off the tree. Would it be spoiled by then?
I wouldn't wait! They may go bad.
What's the variety? If it's an astringent type (e.g. Sabara, Grimal, coronata, grandiflora) then you need to wait until it's deep color and slightly soft, otherwise it'll taste awful.
If it's a non-astringent variety (e.g. red jabo, trunciflora, phitrantha, anomaly) then should be fine to eat early.
Flying Fox Fruits had a youtube video about this that was really helpful to understand. I'd been harvesting Sabara too early and they were nasty. With Sabara, it needs to be almost black and have some give (not hard).