I don't think you can delete packs from the safe. I went on vacation and when I left I had about 30 or so packs in the safe all with $0 left on them. It was about 2 weeks before I got back and went to add some new packs. When I did, about half of the used packs were no longer listed so I assume that after a period of time they just drop off. I have not paid much attention to it since I load and transfer at the same time and don't know the exact amount of time we're talking about, but would guess around 30 days. From what I read in the T&C there doesn't appear to be a limit to the number of packs you can have in the safe, only the total amount of funds in the safe.

I think we can all agree the website (at least) appears to be run by a bunch of clowns and it doesn't make sense to leave money in the safe any longer than absolutely necessary. I personally think the money is safer on the physical card then in the safe.