The hubs usually post their gate information the day before the flight, reflective of the extensive planning that goes into such an operation. The downside is, operational realities often force gate changes several times before it's all said and done.

Between 12-24 hours, the odds of gate information being accurate are at best 50-50, but once you hit around 3 hours prior to flight time, your departing gate info will most likely be good.

It's really a crapshoot. I'd never book a connection at IAH with less than 45 minutes on the ground, especially considering how hard CO tries to get planes off ahead of schedule. At EWR, so long as you aren't out of Terminal A, a 35-40 minute layover is adequate, though the rolling hub structure usually results in slightly longer connection times on the average.