Kick-Off With the Mystery Ball!

Gnomon:     I believe it maxes at around two years, but not exactly since it's rare that your Premium day total will equal exactly that upon purchase. I just tried to max out mine, and I was able to reach 705 days. If you have reached your limit, your purchase screen in-game will look like this (Premium time grayed out):

  That little Exclamation symbol says the following when you max out: "Unable to Extend Premium Account: You will be able to extend Premium Account when 365 days are left until it expires".   

Gnomon:   It should be each match. But, check the times to the right of the matches where it says "CODE AVAILABILITY". That is when you will be able to redeem the code/when they become available.  

Gnomon:   The codes will not unlock until the listed times to the right of the matches. You can currently enter codes from the first two matches, though.    I just tried the MYSTERYBALL code, and it worked for me along with the first two match codes. However, you won't be rewarded until after June 15th, 04:20 PT (even if you play a match today) for the Mysteryball. Are you receiving an error when you enter it the first time, or just not getting the reward?    I apologize for the delay, I was getting clarification on all your guys' questions from our teams.    Let me know if this helps!    Thanks!