I've unlocked them all. You can also get them if you get less then 25k time shards but its not guaranteed. If you go above 35k shards it seems to give you 2-3 party character stickers but you only see one when you open the chest.
Pretty easy to unlock but it takes pretty much one hour of non stop gnome zapping and running for your life. I advice you go to the bathroom before starting the infinity time because once I was about an hour in and had to pee so bad I actually considered wetting myself! I held it in like a trooper though! 🙂
