yes as in how the fuck would that be a desirable combo anyways? if you wanna huff some ether, freon and hand sanitizer at the same time go for it, but fucking coke and dxm?
Yeah I don't see that combo (or anything with dxm for that matter) being very fun.
However, 8hrs is probably plenty of time for you to be okay. There aren't any direct interactions from dxm and cocaine anyway so you should be fine..besides the fact you're shooting coke man.. haha. That's not fine.
possibility of serotonin syndrome. I'd avoid this combo like the plague, and not just because of SS, I think it would be a horrible combination anyway.