Ned has gone up 165 / 11 = <<165/11=15>>15 flights of stairs.
Thus, he has 20 - 15 = <<20-15=5>>5 flights of stairs left to run up.
He will spend 5 * 11 = <<5*11=55>>55 seconds running up the remaining stairs to the bomb.
Therefore, he will have 72 - 55 = <<72-55=17>>17 seconds to defuse the bomb.
#### 17