Bogo Charm of Might... How long is it good for?

[castoff]

Curious about today's BOGO item. The Description for this charm of might doesn't say how long it's good for (1 hour, 1 day, 7 days, 30 days, or whatever).

Does anyone know the duration of the charm offered in the BOGO?

[DemonBlitzKragor]

They last for 1 hour, like every 20% charm of might does.