Twenty minuets of nothing

During my twenty minuets of silence I really struggled to clear my mind. Five minuets into it I found my mind racing with all the things that I should be doing instead of "nothing".  Then I really tried to think of nothing and I started listening to all the sounds of the city which was much more peaceful but still not clear. Then between ten to fifteen minuets I could feel my body start to relax and let go essentially.  Then at around twenty minuets I was almost sleeping and I realized that meditation takes serious trainning to let go of every thought and feeling but still remain present.  I can start to see the benefits of meditation but worry that in my busy life I will not make the time for myself.