To improve consistently,
- Warmup every day. Five minutes is often enough.
- Workout thrice weekly. Forty-five minutes is enough.
- Vocal rehearsals, lessons, and concerts count as workouts.
Warm-ups only remind you how you sing best. They will keep your voice in shape on quiet days and prepare your voice for busy days. By themselves, daily warmups won't make your voice strong, fast, flexible, enduring, or accurate. More on how to do these later.
Workouts will improve the voice, but only if you keep doing them. Doing just one workout a week is enough to tire you and get you some improvement, but several in a week will definitely improve your singing.
Please do not sing far too much. Singing when your voice and body are tired open the door to get bad technique and vocal injury. For beginners, three workouts a week is almost too much. As your voice gains strength and stamina, it will thrive on three to four or even more workouts weekly. Just don't push yourself too hard too fast. The above is going to get you where you want to go.