Above all, you do need to practice daily. Practicing two hours once a week is much less useful than practicing 15 minutes every day.
Whether it is the body or mind, some things just take the time to settle in. Creating a daily practice routine will get your vocal and breathing muscles in shape. Take advantage of the time you have. While having time set aside for singing so you can focus on technique, posture, and breathing is the most effective, that doesn't mean you can't sing while:
cooking
cleaning
driving
showering