the main question you should ask yourself is "what kind of high" do you like?
Should it be more of an "active" head high for during the day, or more of a "body high" which pushes you into the couch and makes you sleep well?
Once you know that, you should look at the strain.. When i googled for banana blaze auto i see it's a "mostly indica" hybrid, so one that will push you more into the couch by default (the basic sativa-indica difference), but not as much as a pure indica would.
When it comes to trichomes you most likely know they go from clear to milky and then to amber.
Since this one is an indica-heavy plant, if you want a head-high, you'd be best off harvesting when around half are still clear, and half are milky.. If you want a body high, then most should be milky and some amber. If 20 or 30% or more of them are amber, it'll just be definitely in the body-high area, pushing you into the couch (and as always, don't wait too long or they'll fall off the plant).
In comparison if this were a sativa, then even even when the trichomes are full milky it should still give you more of a head-high, and to get more of a body-high effect you'd need to wait until there are a lot of amber trichomes.
So it's basically up to you, what you prefer.
happy harvest in either way ;)