How Long Does an Idle Hextech Skin Shard Remain?

Hi, I had a quick question about the Hextech Skin Shard system. I just received DJ Sona from a box, and I was hoping to keep it until I had the required amount of Essences (currently at 1695, but need 2950). Since I'm attempting not to spend any cash on this game for a while, I was hoping to keep the skin shard until I could collect enough Essences to unlock it permanently. So, I ask: Do the skin shards from the Hextech boxes have a duration? If so, how long will a shard last before it is automatically removed from the inventory? Thank you for you time.