Hi, just wondering if anyone can answer. How long should we practice in a day for absolute beginners?

Hey, Stanly! See here for an article I wrote on daily practice: https://www.30daysinger.com/blog/one-lesson-per-day-how-to-practice-for-the-best-results. 

The short answer is: 20-30 minutes is pretty safe to start at, but you can sing up to an hour if you're feeling good and aren't vocally fatigued. As you build stamina and healthy technique, you can extend that time. There's no one size fits all answer; but it's a good idea to start with shorter sessions and increase as you're able!