Has anyone bought WTFast keys and used them months later?

Hi, I'm wondering if anyone has bought a WTFast key, and then activated it 2 months or more later, and if it still works?

I want to purchase some keys from G2A (Paypal Gaming Sale) because it's massively discounted. But I'll be mostly watching Dota 2's TI4 tournament and won't be playing the game I need it for (Aion). So I'm just wondering if it's safe to just keep the keys for until about 2 months later. Thanks :)