I noticed over the last couple mounths that the sponsorship period has been getting shorter and shorter, less than 30 minutes. Today, I activated it and it went off at 25 minutes and change. I thought, what's going on?
Low and behold, the clock on my tablet was about five minutes fast. The game must reference a time server and use that set the end of the sponsorship period. I always figured it just counted down 30 minutes internally. The tablet around five years old and doesn't keep good time anymore, nor does it sync with a network. I don't use the tablet for anything else, so I never pay attention to the time.
Just a heads up for mobile players, you could be shorting yourself sponsorship time. I probably "cheated" myself out of a few dozen sponsored matches over these months, lol!