I recommend an average of 10-30 minutes a day.
I know there are days where you as a parent are tired and there are days where you have more energy.
On the days where I am over-tired I either show them an Instructional Reading Video, I go over Sight Word Flashcards, or I read the story to them.
Most days, I watch the video with my children and then one at a time I have my child read the story to me, with my help. After my child reads each page, I re-read the page to my child so that they understand what the story is about.
If my child needs additional help with the lesson, I will re-watch the lesson with my child and bring out the Flashcards that relate to the lesson and work with my child on the lesson concepts.