Kind of up to the person. Like, I have 2-3 I'm super serious about, and the rest are more things I like to do.
Every Tuesday and Friday evening, from May-Oct, I'm on the water. That's a non-negotiable for me. Then Monday, Wednesday, Thursday and maybe Saturday/Sunday it's other fitness. Jiu jitsu in the winter, running or gym in the summer. Those are my hobbies.
My interests are the symphony, or the aquarium, or the museum. Stuff I can take a date to. Fishing is an interest, not a hobby. Ice hockey is something I'll do for fun, but not dedicated to. Climbing is something I used to do, then I gained weight and now my strength/weight ratio is off.
Hobbies are things I will do regardless of whether I have a partner or not, and will absolutely break up with a partner over. An interest is something I can take or leave depending on how I feel.