Questions on shield/item mods

Let's say I have a shield/item that reduced crippled duration or any other duration....

Does this effect only kick in if I had the shield/item equipped prior to receiving the condition, or it would still work if i equip it while already being under the effect of the condition?

When you answer, please tell me how do you know this. Otherwise how do I know it's true?

The reduction only takes effect if the item was eqipped prior to receving the condition. It's well known and has been tested. Quite easy to check for yourself as well.

Thanx...