I am having the same issue; it seems like there are two sliders in unit frames > raid > debuffs for 'count font size' and the 'duration' option leads to the cooldowns tab, but none of the sliders in the cooldown tab for unit frames actually effect anything on the raid frames.
So, after checking the discord it seems the only way to make debuff duration show on raidframes is by making the icon bigger. 20 is minimum apparently. If your raidframes had smaller icons you'll just have to change it. Sounds like it's intended.
I've been hoping it was a bug, and had been looking forward to an update. Changing the icon size to at least 20 causes the timer to appear again. Unfortunately, this totally screws with the aesthetics of my party frames, but I'll adjust things for now I guess. As a healer, it's imperative that I see the actual cooldown on party frames.