When I was doing a long trip in the US in a C182, I just leaned it till it went rough then enriched a bit. That will get it close enough without having to wait for the temperature gauge to settle.
The problem with that is that you might just end up more or less at 50 ROP, which will be hard on the engine and run the CHT way up a few moments after lifting off.
Therefore, I prefer the method using known fuel flow values. There Cirrus has a small table in the POH for that which is also printed on the RH side dashboard. If you don’t have such for your aircraft, then, I agree with the other, just work one out yourself using 150-200ROP in a climb.
Of course, the fuel flow method only works if you have a (working) fuel floelw gauge.
It also depends on the engine. The IO-550 I can lean a long way before it goes rough. Leaning to rough and richening a bit I’d still be somewhere in LOP territory.
