Duration refreshes itself when the Thief takes damage.
Condition damage doesn’t refresh the Revealed effect.
To balance the fact that constantly attacking the Thief will keep the Revealed effect up, also would like to change the Revealed effect to behave like the Blind condition for stealth:
Revealed
Causes your next stealth attempt to fail. (Failed stealth cures Revealed.)
So if the Thief opens up with an attack from stealth and wants to jump back into stealth, he’ll have to…
Avoid direct attacks or damaging AoE for three seconds. This can be done by dodging, applying blind to the enemy, shadowstep away, etc.
If under constant attack, use a Stealth skill to remove the Revealed effect, then use a Stealth skill again.