After today you will continue your process of randomly selecting the amount of cubes you have earned this month until you are lucky enough to get your key. You must continue doing any of the daily tasks you are currently doing if you wish to keep that cube or it will be struck off your cube allowance as usual.
So if you only have two or three cubes you could be limp and locked up for a long, long time. I will however give you the opportunity to double your cube count. If you have a lot the gamble may not be worth it to you but you can still take it if you want.