The time isn't an issue at that level. They have specific tests for various situations and the time it takes, it takes. I've seen banks spend upwards of 6 months testing before instituting software changes to trader/production systems.

As for capable IT departments, on the large corporate scale, they fairly bulge with competent people. Obviously not everyone's a star, but they don't suffer idiots to live.

I don't upgrade anything until it's been on the street for a time. I let other people play canary.