Clearing the customs by 11 am then getting a taxi to drop you off at a bus terminal, then taking a bus heading towards Batangas Pier in order to catch the 4 pm last ferry out for Puerto Galera, hmmm, its feasible. But in any event, I suggest you have a back-up plan, in any case.
Ordinarily, travel time all in all is between 2 1/2 to 3 hours. But that presupposes no heavy traffic, stop-overs or waiting time. From the airport to the bus terminal, expect to encounter minimal to heavy traffic which can set you back by 30 minutes. Upon arrival at the bus terminal, the bus you will be boarding on will not leave immediately as it will still have to wait for sufficient number of passengers before being dispatched bound for Batangas Pier. Waiting time then at the bus terminal can be as short as 15 min to an hour. Along the way, it is normal to expect traffic along the south superhighway considering that the skyway at alabang portion is under construction, plus the fact that at the time you are seated comfortably in the bus trekking towards your intended destination, trailers and other trucks are likewise allowed to travel during that window period (between 10 am to 4 pm), thus contributing to the traffic conditions. In addition, buses inasmuch as they are a profit-oriented business would try to pick-up as passengers along the way, as well as try to get as many additional passengers as possible during stop-overs. So expect to be delayed by an additional 30 min to an hour along the way.
Considering the above, I'm pretty sure that from the time you clear the customs and until you reach Batangas Pier, you'll be pretty much agitated, uneasy and always at the edge of your seat, anxious and worried that you may not be able to catch the 4 pm last ferry ride at Batangas Pier. So just in case you fail to reach Batangas Pier, be prepared to stay at a traveller's lodge at Batangas City. I suggest you make a research and find out where you can stay overnight in case you fail to arrive at the Batangas Pier before 4 pm and just take the earliest scheduled ferry out the next day.