and i was in bed when the shop games gone live and the one i’m interested in is already sold out. 
I knew i should have stayed a little longer awake yesterday.
mehh, then i’ll have to wait for the next refill and hope that there will be a game which i’m interested in AND which is not sold out when i’m noticing the games are up.
You are not the only one
I think the reasons why the time between each refill is intentionally vague, is for similar reasons as to why PAX badges go on sale without warning. Demand needs to be controlled and giving us an early heads up (beyond the newsletter notification) could be exploitative. Or we might accidentally flood and crash the site. Well, I don’t know the methods on how to game the system, but I feel like it may have something to do with exploitation and demand control.