Magic item powers with no duration?

[MatthewJHanson]

If a magic item power has no specified duration, how long does it last?

Specifically I recently obtained an amulet of passage from LFR module CALI 3-3. And it has the following power.

Power (At-Will): Standard Action. You attune an ally to the Amulet. While attuned and within 10 squares of you, an ally can use the Amulet’s powers (but not its enhancement bonus or properties) as if he or she were wearing it.

Some of my fellow players and I were debating how long power should last. Could I use it before any battle broke out to attune my whole adventuring party?

 

[OnlineDM]

Personally, I interpret that power as lasting until the next time you use it. So, you can attune one ally at a time, and they stay attuned until you switch to a different ally (months, years, whatever you like).

 

[Dice4Hire]

There is strong precedent for all magical item abilities and powers to cut off in 5 minutes also.

 

[CAFRedblade]

I don't think I've come across a specific limit, but for an item like this either of the above could be argued, or simply require it be re-attuned every day.

 

[keterys]

Instantaneous. You've attuned them, congratulations.

Now when you adventure with them, they can use its daily teleport.

 

[Fkewl]

Instantaneous. You've attuned them, congratulations.

Now when you adventure with them, they can use its daily teleport.

Yup, we play it exactly like this : once attuned, it's forever

 

[Ferghis]

Instantaneous. You've attuned them, congratulations.

Now when you adventure with them, they can use its daily teleport.

This.