How much is the minimal time for practicing Vipassana in daily life for achieving better mindfulness? How much is the minimal time for practicing Vipassana in daily life for achieving better mindfulness? Is 30 minutes enough?

I ask this question because I currently have some trouble being mindful, and (I think) it has become the source of many problems. If 30 minutes is not enough, perhaps you can give some suggestion based on your experience or the suttas.
Geez, ya'll are crazy. 30 minutes?
I'd say WORK up to that maybe after a few months of practice but in the beginning it is best to LIKE MEDITATION and do PRACTICE PROPERLY rather than just loiter around and try to sit tight for 30 minutes thinking about Jane and Bob.

I have had 3-5 minute sessions where you would NOT believe how much baggage I dropped and how refreshed and happy I felt.
And then I've had 30 minute sessions where I came out worse than I went in, because I was obsessing over thoughts instead of taking time to write them out and therapatize myself.

Meditation is NOT the time to therapatize oneself, so make sure not to get stuck in that habit!
If you have 30 minutes, use 20 minutes to understand how to meditate and journal and get rid of your baggage and then 10 minutes to meditate perfectly, dropping all things away and just being mindful of your object (breath, thoughts, or whatever else) the entire time as cohesively as possible. Repeat until you can do that 10 minutes. You will feel an enjoyable buzz and a helpless smile and lightness if you practice correctly.

At my current stage, every session (morning, pre-lunch, evening) I have doing 3 20-minute meditations, each with a different meditation object that I have chosen. I have a 1-5 minute break in between each object.

For beginners I would reccommend 5 to 10 minute sessions. When you ACTUALLY meditate that long... increase it by 5 minutes. When you LONG TO MEDITATE longer, increase. Do not force yourself to sit too long. You will idle.
Instead, put your energies into meditating properly and perfectly for a few minutes. This will increase your mindfulness, because you don't have as much time to fool around."

Nonetheless, don't let what I am saying stop you if you yearn for long periods of time! You will not attain samadhi unless you practice for HOURS at a time. So if you feel like you can actually pay attention that entire time... godspeed!
But above all else, do not scare yourself away from your gradual climb in meditation abilities by making meditation frustrating. Enjoy it and do not underestimate the Power of Less is More.

Let me leave you with this excerpt from a Buddhist book I am reading "Mind Experiment":


  "It is better to meditate often for a shorter time than for a long
  time but infrequently. To make real progress, meditation should become
  a vital part of one’s daily life. Meditation masters recommended to
  their students: “Do it with an aspiration so strong that it will be
  the cause of fulfilling your provisional and final aims. Meditate in
  this way during four sessions: predawn, morning, afternoon, and at
  nightfall. Furthermore, if at first you meditate for a long time, you
  will be readily susceptible to laxity and excitement. If this becomes
  your habit, it will then be difficult to correct your awareness.
  Meditate in many short sessions. If you end your session while still
  wanting to meditate, you will be eager to reenter each future
  session."