20 minutes with no ads is rough, but OT hockey is compelling tv, which should make banner ads more valuable during that time. They could always negotiate in extras for that. Plus, if you go through one 20-minute OT period, you could always chop the next into 15 or 12 minute chunks, with a more brief intermission so you run 2+ minutes of ads right after the period, a brief studio report and then more ads before starting up the next period.