I'm with church haze here. Once I learned how to grow and had a few nice harvests under my belt I stopped checking trichomes. I started to notice how drastically the calyxs swell the last couple weeks, and the plant will take on a very finished glow. One of my strains turns completely purple right at the 7.5-8 week mark like clockwork and I know its got about 2.5-3 till its ready. The other one the branches all start to get overweighted, even the little buds flex down as they plump.
I see lots of trichomes on that plant, so I don't know why your saying its not frosty. I can tell from this one picture its a sativa dominant hybrid plant. Its got that typical leaf structure, and the smaller sativa trichomes. The bud structure and leaf shape remind me a good bit of a White Widow I grew for years.
I would bet money any amber trichomes your seeing were either the earliest few the plant produced, or were damaged at some point causing them to oxidize. That plant is still growing fresh calyxs, and hasn't even started to plump yet. I think that plant will definitely go for between 60-70 days to get the best results both from yield and quality stand point.