If your airline flies into Hobby, this is genuinely the easier of the two airport-to-cruise routes.
Of the two Houston airports, Hobby is the friendlier option for a Galveston cruise — it sits on the south side, meaningfully closer to the coast than IAH.
50-60 minutes is the typical range, roughly 20-30 minutes shorter than the equivalent trip from IAH. Mostly highway once you're past the initial stretch out of the airport.
If your airline flies both airports, and Galveston is your destination, Hobby is generally the smarter pick purely on drive time — less time on the road, more buffer for everything else.
Even with the shorter drive, we'd still suggest 3-4 hours before your ship's boarding cutoff — terminal check-in can take longer than the drive itself on a busy sailing day.