This week, until end-of-day Friday, the surf timer will be reduced by 3 seconds. For free members this means a 9-second timer, for Diamond members this means 3 seconds, and other upgrades are somewhere inbetween.
On the last day of the timer reduction, the surfing bonus will be doubled. Your surfing bonus is determined by how much you have surfed in the few days before. So to get full benefit from the doubled bonus you will need to surf lots on Wednesday and/or Thursday. You can always see what your surfing bonus is today, and what it will be tomorrow, on the member's home page.
Make sure you surf plenty this week so that you have a bonus to double - it would be a crying shame to have a bonus of 0% on Friday!