I have a friend that can really work 4 hours a day, but he is a special case where he does not have a family to upkeep and no mortgage. He is also a bit hard on the frugality.
But finding such person is basically 1 in a million. If I post a job with 4h a day which amounts to 1/2 of a normal salary I will probably never get a candidate. If I post a job with normal salary and then start explaining that it is 1/2 hours and accordingly paid, some people will get angry.