Rule 21.3:
"If, due to suspension of play after the start of the
match, the number of overs in the innings of either
team has to be revised to a lesser number than that
originally allotted (minimum 5 overs), then a revised
target score should be set for the number of overs
which the team batting second will have the
opportunity of facing, this revised target being
calculated by the Duckworth/Lewis method. A par
score will be set for the second innings. If this is
exceeded a win for the team batting second shall
result. If the par score is equalled then the scores are
tied (see 21.5, 21.6, 21.7 and 21.8 below). If after the
restart of play it is discovered that the wrong
Duckworth/Lewis target has been set the faulty target
shall stand"
http://static.ecb.co.uk/files/3140-fc-domestic-friendslife-t20-2013-p87-108-lr-12372-12372.pdf