Boracay is such a small Island, the length is only around 6 kilometers and width less than 4 kilometers. Thus riding the entire island will not take you more than 3 hours in one continuous sweep. Half day or whole day would give you ample time to ride and explore the attractions on each major destination point.
There are bike rentals available for hourly, half day, daily and weekly rates. The price listed are for tourist and as locals- you can actually haggle for a lower cost. In my case, I paid 600 Php (2014) for a half day rental. I rented at Leonardo’s which is a small stall located in front of D’mall- its the only structure within the small lagoon area. Note though the most bikes, are not properly maintained. The one I had has no front shifters.
Notable places to visit-
Then from Bulabog, you can go to the other end of the Island and make a loop towards the pier/port area. There are also other small access roads to lesser known beaches that you can explore. On the way to Bulabog- you can take the Mount Luho road, the highest part of the island with some more challenging short climbs to make the island ride a little less boring. Mt Luho has great view points in the island.
Enjoy your beach with a little bike ride !