I have done the drive to Tha Dan from Krabi Town and going to Khao Phing Kan (JBI) by longtail boat arranged at the pier. That is a full day by motorbike, sunup to sundown. You stop for drinks, photos, snacks, waiting for downpouring raincoluds to pass (10 or 20 minutes). You are lucky to get back before sunset when the truck-trains start taking over the highways. Anyway, it is possible, and enjoyable with travel in daylight hours. I have to recommend it, but give yourself plenty of time starting early in the morning. With arrival at 1:25PM (at Krabi airport?) I don't think it is possible to get to your hotel, rent a vehicle, and drive there for the last freelance longtail let alone get back at a safe and reasonable hour.
I have done a tour from Phuket also, with Sim's tour. The A/C on the bus was less than minimal; but it was a good tour overall. Anyway Khao Phing Kan is nothing to shout about. With the freelance longtail boat I wouldn't even want to set foot on the island as it comes with a 200 baht price tag for the park fee. It is better to just go around and snap some photos from the boat. By tour, the fee is mandatory and included, and with or without fee there is no less expensive way than Sim's tour from Patong. So you may as well get off the boat.
Well it isn't Khao Phing Kan you should be interested in. It is the whole of the marine park there. That is beautiful with all the limestone outcroppings. It gives such a feeling of a foreign place; or at least it did for me before I was living in Southeast Asia. But you have to go by longtail boat. With those big tour boats and sea kayaks, I doubt you could get anything close to the same experience. Well you are from Malaysia so the whole experience isn't that different than an island hopping tour in Langkawi, except for the James Bond thingy, a famous natural landmark, but not such a big deal.
And Phi Phi smells like the name. Lots of raw sewage like in Loh Dalam Bay a real pee pee festival there every night as toilets are insufficient for the masses. And there are lots of rude farangs and locals in the village. That stinks too.