Since Spirit changed the flight would you qualify for a refund to give you more choices of other airline flight times?
Galveston to IAH is 70 miles.
If everything clicks in to place with no problems, you could make it, but there are just so many pieces that have to go just right, personally, I wouldn't chance it.
I'm local, there are just too many things that can go wrong. Fog in Galveston, Houston's infamous freeway traffic congestion, IAH having flight backups, etc. There have been thousands of flights cancelled this week due to the freeze. We just aren't set up for inclement weather.