The FIRST TWO DAYS-20 seconds. The THIRD AND FOURTH DAY-30 seconds.
On DAY 4-30 seconds, and on the FIFTH DAY-40 seconds. You will REST on DAY 6.
On the SEVENTH AND EIGHTH DAYS-45 seconds; DAYS 9-11 hold for 60 seconds.
On the TWELFTH DAY-90 seconds. DAY 13 will be a REST day.
Resume on the FOURTEENTH AND FIFTEENTH DAY for 90 seconds; DAYS 16 and 17-120 seconds.
On the EIGHTEENTH DAY-150 seconds and REST again on DAY 19.
DAYS 20 & 21-hold for 150 seconds; the TWENTY-SECOND & TWENTY-THIRD DAYS-180 seconds.
DAY 24-hold for 210 seconds. REST on DAY 25. On the TWENTY-SIXTH DAY-210 seconds.
DAY 27-hold for 240 seconds and on the FINAL DAY 28-hold the plank position AS LONG AS YOU CAN.
Source : Sun-gazing.com