Is it a sin not to repent every day?

In simple terms, to repent is to turn back toward God. There are some obvious sins, however, anything that turns us away from God, leads us astray or otherwise causes us not to think about Him, is sin. Technically, anytime we do wrong we should feel deep sorrow, acknowledge it before the Lord and ask for forgiveness. Repenting daily just to repent would be an act of legalism and useless if it does not come from our innermost being. What God is most concerned with is the condition of the heart. Is it bent toward Him or wayward? Is it troubled when sin happens or oblivious to it? Kind David said it best:

Search me, O God, and know my heart;

Try me and know my anxious thoughts;

And see if there be any hurtful way in me,

And lead me in the everlasting way. PSALM 139:23–24

I submit to you that if a person prays this prayer and really means it, repentance, daily or otherwise, will become a moot point because the ultimate goal is not to sin in the first place.