Hello
You're looking really good so far, buds are developing nicely. The pistils changing is an important sign that they're maturing, but still a while to go before over. They'll be able to help tell when ready and to flush without the loupe. Try to aim for them being about 60% colored and curled when you start flushing.
Not having a loupe isn't such a big deal, if you just try a variety of photos, with good light, zoom in, try using the flash etc you should get enough of an idea on your trichromes...not perfect of course but useable enough to know when to harvest.
Most of my autos usually flower somewhere between 6-9 weeks, and with your pistils still being mostly white, I'd say wait a week or two before starting the flush. Keep an eye on the pistils and how quick they change and then keep playing with the trichrome photos.👍