As already mentioned before I consider the pre- and after-dive time as most dangerous for a housing. I own an Ikelite housing for my Sony A65 and I am always really afraid that something goes wrong before or after the dive. This is mostly the case when I'm using the 8" dome which is really heavy as I am pretty mistrusting those four funny port clips which I tighten from time to time when I do a lot of dives.
As soon as I am into the water I am not afraid anymore because water pressure will keep everything together. As I am always very carful when assembling everything I am never nervous as long as I am underwater.
So for me the dangerous phase is before and after the dive