I know it's probably very strain dependant, and quite hard to gauge due to different buds maturing at different rates, but is there an average time of trich's changing from clear to milky to amber?

Understand there probably isn't a clear cut answer, but everybody's experiences might show some sort of trend.

Well, "clear to milky" is preetty meaningless, since they're clear from the outset...
I found that (very roughly) 50% milky to 50% amber takes about two weeks. A bit quicker if indi-dom. Can be as quick as a week. A bit slower if sat-dom.