Well that was recommended by my sheikh. I think when we fix to some minimum content, as time goes, this can be increased as one gets more attached to the Quran but one should be keen that one reads atleast 1/2 a juzz every day. This will have its own barakah if we are steadfast but the same can be said about fixing time too may be. And as far as time, if I am too tired, I kind of recite slowly and take more time to recite 1/2 a juzz. So it all depends on the person. Anyways different things work for different people. Some can fix the time and some the content. As long as we get the tawfeeq to recite Quran everyday then Alhamdulillah. The main thing is to remain steadfast on whatever we decide I think. Allahu alam