Neutral setting would be your normal bite position – your jaw has advanced 0 mm. I have advanced my jaw 5.25 mm forward from my normal bite position. It sounds to me like 3.5 -4.5mm in 2 weeks is advancing way too quickly, this may give you jaw problems. What device do you have and what directions did your dentist give you? You typically want to advance .25 mm forward once every 3-4 days. That’s why it takes approx. 2-3 months of patient, slow adjustments to reach your max. This website
www.talkaboutsleep.com has more discussions about oral appliance on their boards just to let you know.