I find it it very interesting that you always come into these custody (for want of old terminology) threads, considering you have no experience whatsoever in this area. You are all about parental rights, whereas what's in the child's best interests is not necessarily (or even mostly) to spend equal time with both parents. Have you even read up in this area?
The OP posted because her DS is struggling and unhappy in this arrangement. His dad is hardly available yet he spends 50% of his time at his dads house. That in itself makes the arrangement ridiculous. As a SM myself I think it's heartbreaking and I'd never accept such an arrangement for my DS! His dad is wrong for insisting on the arrangement just to get his fair share (or to hurt the mother which is just as common).