[Coda]

It's a question of HP, not of time. The "RES" icon means that the monster will survive being one-shotted, like the Resolve leader skill of the ogre-type monsters. When the boss is dropped below a certain threshold (for most bosses, it's 50% or 75%) the icon goes away, and if they heal up, it comes back.

Most bosses with Resolve also have powerful abilities that trigger at very HP in order to punish you for triggering it. Some bosses just heal to full; others will multistrike you for huge amounts of damage or use a gravity effect and then hit you again. Be careful; these abilities key at HP ranges, not off of triggering Resolve, so if you wear them down into that range without killing them, they'll still use it, so the recommended strategy is to do the lowest amount of damage that will get them past the threshold and then spike them the rest of the way down.

According to PDX, Sha Wujing's threshold is 75%, and his retaliatory attack is a 99% gravity followed by a 19k-damage 2-hit attack. Hit him with a couple of 3-matches to soften him up before spiking him down the rest of the way.