It depends if your current temporary visa will still be valid during the processing of your resident visa, interim visas are not issued for the processing of resident visas so you need to stay legal during that time. My partner applied for her residence based on partnership 6 weeks before that date of our 12 months together, so yes its fine to lodge the application before the 12 months is met, as F2.35 in the immigration operation manual states
"F2.35
b.If, after assessing an application, an immigration officer is satisfied the couple are living together in a partnership that is genuine and stable, but the duration of that partnership is less than the 12 months required, (see F2.5(a)) they may defer the final decision to enable the qualifying period to be met."
See here
http://onlineservices.immigration.go...ual/i30880.htm
Speaking from personal experience, we also wanted to get the application underway before our 12 months living together to reduce the need of applying for a further temporary visa.