How long will 5 units of Botox take to wear off in upper forehead?

A "standard" botox treatment in the upper forehead will last 3-4 months. What don't you like about it? How it looks? How it feels? It is not unusual for it to feel a little strange at first but that will improve with time. If it's asymmetric it can be fixed. Although, that would require more botox.  
You received a very small dose. Typically the upper forehead is treated with 10-20 units. So I would expect that you'll start seeing it wear off in 4-6 weeks with full resolution 8-12 weeks. 

Thanks for your question.  For the forehead, the strongest effect typically last 4-6 weeks before it starts to fade.  Usually by 3-4 months it is completely gone.