Can't tell you the ferry schedule, as there are different companies and variations with time of year. In the off-season (winter), you’re lucky to get one ferry a day (you have to stay overnight), but in the summer season, there are several trips a day by multiple operators. I don’t know the date cut-off from off-season to season. Here is some info that I’ve been meaning to share, but never got around to before. Note that all of the ferry info is in Chinese. If you zoom in on these images a little, they are still readable.
Info page of brochure – one ferry company:
http://img157.imageshack.us/img157/3405 ... fo18to.jpg
Photos from brochure – first ferry company:
http://img157.imageshack.us/img157/1953 ... es18lm.jpg
Info page of brochure – another ferry company:
http://img140.imageshack.us/img140/6486 ... fo21jv.jpg
Photos from brochure – second ferry company:
http://img157.imageshack.us/img157/14/g ... es22dn.jpg
Contact info from Tourism Bureau:
http://img140.imageshack.us/img140/2231 ... nfo4lj.jpg
Map of Green Island:
The trip is about 50 minutes one-way.
Prepare to puke on the ferry or to do something specific to avoid it.
Hope it helps!
P.S. – If anyone has similar info for Orchid Island and is willing to post it in an appropriate thread, that would be great.