I haven't looked at it in too much detail... But I think Slicer automatically heats up the bed and then starts the nozzle heating. I could be wrong on this because I haven't spent the time to dig in, but I think it then pastes your Start GCode into the file. After your Start GCode it issues the command to wait for the nozzle to be at temperature. So it isn't like my GCode was doing everything I said it was doing. It just works out that way.