If you want to make changes to your voice in a few months, practice as often as possible. Every day or every other day. If you're working to increase your endurance for regular performances, you'll need to increase the length of those sessions. Singing students usually practice two hours or more every day.
That doesn't include time spent learning to sing at first sight, dictating, playing the piano, and absorbing knowledge related to singing, such as anatomy, music theory, and music history. Trying to schedule more than once a week would be ideal. If you are a practicing musician; for example, if you have several residences or go street music every day, then it is true that the more often you have classes, the better it will be for you.