23 minutes...which tells me you were really impatient. I can see someone saying this guy took about 20 or 25 minutes. But to be precise at 23 minutes, tells me you were watching the clock. What did the guy do to take so long? Did he dump,refill, dump again? Flush it out? Some people like their tanks clean.
Unless there are any rules posted, I don't think it should matter how long they take. You either wait or leave and dump elsewhere. That's part of many sites sharing one dump station. Don't fret, you may come across this again.