Yes second crack is very hard to hear, hold you ear over the chaff collector if you need too then wash your hair if you dont want your pillow to smell like coffee smoke.
The GeneCafe is sensitive to bean mass and amibient conditions so its probbably pointless giving you a specific profile for a PNG. However it is a relatively easy bean to roast and get good results with.
When your starting out 250gm at 225c for 18-19 minutes is pretty safe and should be ballpark second crack. Dont take my word for it though sometimes things can happen faster.
I would suggest that in the gene cafe for most coffees its safe and often a good think to start the cooling cycle before second crack. *Once you start hearing second crack your going to get a darkish tasting roast.
There are a few signs to look for that your going to hit second crack soon. These might include an increase in smoke, the smell of the smoke changing from a toasty coffee smell to a more sour burnt toffee/coffee smell. Visually the beans will go from having a mottled uneven surface to a smooth almost glossy appearance.
Im not taking any responsibility if it catches fire, but If your new to roasting I recomend sacrificing a batch and roasting just a little bit darker then you think you should or untill you see some oil on some of the beans. This should give you a complete idea of the various different stages of a roast.