I think this may be a bit harder than it seems. The problem that I'm seeing is that you want the object to do something no matter where it is. I'm thinking that you cannot load an object into a container although it's possible that I'm thinking of different code since I play with various codes and get easily confused. You could purge it in a container but I don't think you could replace or transform it.
It may be possible to simplify. You probably want this mask to do something until a certain time and after that time to do something else. As a mask, you probably want this to happen while it is being worn. Why not put a timer on it to set a variable after whatever time. Then check to see if it is being worn. If it is being worn, hmm, I dunno if you could silently switch it.
Okay, I tested this and, yes, it will transform silently. It amused me to use a food item as the transformation and to see my test character was wearing a chestnut on her head. However, the trigger will exist on the new object. You can get around that with a vnum ifcheck. The trigger did not work if the item was in a container.
If the item is not being worn, run the trigger when someone puts the mask on since you probably didn't want to do anything with your mask until then. Check for the timer variable and switch or don't switch, depending.
Your trigger is probably totally different than what I'm thinking and this has nothing to do with the question but this may provide a jumping off place for you.