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Once I get the initial fire going for low&slow (dome and bottom vent open) about the size of a grapefruit, I load the platesetter, drip pan and grate shut the dome and adjust the vents to about the target temp (somewhere 250-270). Wait til temp is stabilized for a good 45 mins or so, then add the meat and away we go. As xraypat23 mentions, I mix chips throughout the lump load.
The 1.5-2Hrs/# comes from cook run times-always estimate long and then use the FTC if finished early. With an average of around 250*F on the calibrated dome I have never had a butt or brisket (flat) come in at less than 1.8 hrs/# and most are in the 2-2.1hrs/#. enjoy the journey.
I'm with @lousubcab. Load the platesetter as soon as the fire is lit. The platesetter is going to affect the way your fire burns and your egg temp. Also, adding a hunk of cold ceramic is also a heat sink, which will temporarily bring your temp down if you add it after you get to temp, which could cause you to over react and overshoot your temp.