I understand how many mothers of "big boy/gal" feel when it seems that their kids are stuck in PN wasting one year. I went through the same struggle too, and eventually I have come to a conclusion that maybe it's better for the kids to do PN first then pushing them into K1 (regardless of they get accepted by the school or not).
You may let ur son to have N class starting from Jan next year, I do the same, my son will have 1.5 years N class. He is so "mo liu" at home. I want him to play with the others sharply at 2.
Half day for the first half year, I still have not decided whether to change to whole day class for another year, it depends on whether he can adapt well there. I am afraid he will get sick easily if he attend whole day class sharply at age 2. Teachers there also recommend us to attend half day only for N class. They are too young la.