Setting up a business model for becoming a life coach

Question: How long are typical coaching sessions? I only know the 20 minute session(from self coaching), but I was thinking they would normally be around 1 Hr? I am trying to set up a business model for myself on how long it would take me to recoup $18,000 if I only worked part-time; I know $/hr varies, but for business model purposes, I am putting in $40.00/hour. Is that a “reasonable” amount?