Ideally, if filled and let sit with the battery in and no drawing at all for 2 minutes, the contents of the bowl should turn very dark brown (and perhaps black on the bottom). We try to calibrate it hot enough so that it falls about 36F (20C) short of actual combustion under these conditions. If you shake/stir the Box (but do not draw or open the lid) during this test, you will get a better sense as to how the heating is occurring. Depending on the specific load (how dry it is, how finely ground, etc), the specific calibration of the particular LB unit and assuming zero draw rate conditions, actual ignition conditions might be achieved in as little as 30 seconds. For most units shipped under most conditions, the time will be noticeably longer.
During normal draw, the Box should be hot enough to create vapor when looking at the draw hole, but not to obviously create large visible clouds (it is not designed for that). If you can see the vapor on exhale, it is either wasted vapor or smoke—both conditions to be avoided. Really, the best test of the Box is how it delivers the medical qualities of the herb—what the user feels like 3 minutes after taking a few draws, rather than on what can be seen when exhaling or what is felt in the first 30 seconds or so. Also, if after taking several hits (with shaking in between) the contents are all brown, then it is certain that all available vapor has been created, and presumably ingested. If the contents are still mostly green after several draws (not just some green specks) and are not mostly brown, then there is a chance that the Box may be running a bit cool (else, check the battery charge and slow the draw rate).