Sugars are caramelising IIRC.
A roaster I know told me I should aim for 6 minutes.
I usually manage around 5 minutes give or take a few seconds.
I try to stop just before SC on the PNG Kimel I mostly roast and guage by temp readout together with smoke etc
You need to be careful after FC or the temp will rise too fast.
I usually start lowering the heat source at FC to slow down the temp increase but keep it rising.