Part 5:

The nudge test will be your best friend here too. No matter what your thermocouples say, unless the solder has melted under the chip, you have not reached 217 (lead free) or 183 (leaded) under the chip.

The nudge should be more of a slight/push down on the chip to see if the solder is melting/melted. After you see movement, give it another few seconds (6, 8 , no more than 10) before you move your nozzle out of the way and pick the chip with the vacuum pen.

With a great deal of practice, you will be able to tell by the sound/feel when the solder has started to go liquidus, and even be able to control your nudge well enough to use it when you attach chips (VERY difficult to do until you gain the skill necessary to nudge the chip, and not apply so much pressure/movement that you cause bridging of the solder balls under the chip, or move it too much)

Good luck, have fun, but above all... STAY SAFE !!