This is somewhat dependent on the strain/batch, I've had a few strains that don't seem to produce much vapor (the Platinum strains [Platinum Bubba, Platinum Cookies, etc] and some Hazes) and others that just won't quit, even after a good 12 minute session. Not sure what your tech is, but I prefer dry herb to moist/fresh out the bag herb, medium to fine grind. Load my GonG and set it on my piece, turn my Solo on to preferred temperature, place on GonG, and let it heat soak for 15 seconds or so. Usually if I keep an eye on it, once it reaches temperature, I don't hit it until it goes through a "heat cycle" (when the heat light turns on for a bit). THEN I take a pull. First hit's tasty but not much for vapor, 2-5 seem to be where it's at. Also, vapor is thinner than smoke, so don't be surprised if it doesn't look like you just milked a cow into your glass
I've found myself surprised when shining my iPhone light right next to my glass, seeing how dense the vapor actually is compared to room lighting. I can get satisfying vapor production through glass as low as temp 3, but usually if I'm using glass it's because I want to cool and inhale a significant amount of vapor, so I'll maybe take a dry hit or two on 3, then go 4 for a hit, 5 for a few, 6, and then 7.