If you didn't know when the enemy would swing his weapon in Oblivion, you have some pretty bad reaction timing
I mean, it's too easy. I don't know how someone would "fail" at timed blocking, at least as far as speculation goes.
:shrug:
As I mentioned, I'm not the greatest "twitch" gamer. I don't do games like Devil May Cry / Bayonetta / Ninja whatever. I was terrible at Street Fighter II, back in the day. I've played some RPGs that had timed-button-press defense features..... and generally ended up not doing well with them, depending on how picky they were (Counter mode in Magna Carta:Tears of Blood, for example.)
Oblivion? I turtled behind my shield until the enemy did a swing-recoil, then dropped the shield to do a quick swing or two. Then back to turtle. With the periodic heal spell to counteract the damage that always leaked through a shield block.
So yeah.... I'm a bit wary of "timed blocking".