I think it's clear to all thinkers that, the reason for delaying the ceasefire was to give Israel time to obliterate some very important military sites in Gaza that they had pinpointed. It was a moment of weakness on Hamas's part and they took their eye off the ball. The bus attack would've happened in any event and, the fact no one was killed, makes it less significant in military terms.
Shaffir to Herzog: Opposition failed to show leadership in political battles against PM (Haaretz)
from the article: A cease-fire that could have come earlier