Oh, there absolutely is. But most hobbies people seem to have are just pointless and waste time.
1. an activity done regularly in one's leisure time for pleasure.
No doubt these posts could be your hobby; you do it for pleasure but it's otherwise just a pointless waste of time.
"It's not a waste of time since the primary purpose is enjoyment" — in that sentence you place enjoyment above any other benefits the activity might have (but most often does not). Hence, it's a hedonistic approach.
Enjoyment here is a sufficient justifier within that domain, not in a life-wide philosophy. Labelling it "hedonism" is a significant overreach.