Hello Shiva and thanks for your post.
Regular mindfulness practice is important. Many people ask me this question as we all live very busy lives and it can be hard to find time to fit practice in. My recomendation is to set realistic goals regarding your practice. Consistency is also necessary when it comes to mindfulness. Five minutes per day is actually better than one hour once per week. Start with what you can do and slowly increase it. Also sincerity is a key aspect. Understand what your are doing and why you practice. If you know what and why you are doing practising mindfulness you are much more likely to maintain your practice in the long term.
You don't have to practice mindfulness at the same time each day. However starting mindfulness practice at the same time will help your mind and body to get into a regular pattern of practice. In other words, it might be a little easier if you do keep the time similar.