You have got to stay in PP. My fav. place !
So here's an idea,
Boat to PP - 200BT or 600 return
Stay on PP for a couple of days - dive , drink, dance, drift
boat to Krabi - 400bt return
back to PP in morning, then catch afternoon boat to Phk
boats leave to pp - 8.30 1.30 & sometimes 3
9 am pp to Krabi
Dunno about krabi times but there is a morning boat - suspect it's 8am ish
PP - Pkt - 9.30am or 2pm
enjoy