Honestly it really depends on what your schedule looks like and how your child responds to structured time versus free play. My girl was the same age when I started trying to do some simple worksheets with her after work, and I found that a short 15 to 20 minute session after dinner worked better than trying to do a long stretch. Some mums I know prefer to use the weekend mornings when everyone is more relaxed and not rushing. The key is to keep it consistent but not too rigid, because at 4 years old the attention span is still quite short lah, so small and frequent beats long and stressful any day.