It's a matter of tactics, it would be foolishly short-sighted to rush things and reveal to the world (and to the Egyptian army) their true colors. Better to wait until they have cemented their position as the rulers of Egypt. Nevertheless, I too, hope that they will not break off the treaty.
IDF strikes Gaza targets in response to rocket fire (Haaretz)
from the article: Egypt's radical Islamist party vows to respect peace treaty with Israel