Cancer's time extends to July 22nd or 23rd. Therefore one or the other hemisphere of the planet is facing the SUN while it orbits. That, only, sets the boundaries of the Signs not a certain number of days.
Crabs have a very hard shell and pinchers.
Remember Crabs bite, they also have their home hidden away in a hole someplace and they are always taking food back home with them. Cancer is FOOD and LOVE, the two parts of most basic survival. We all need them. Cancer's favorite room is the kitchen. Cancer is very sensitive and sometimes psychic.