Use the range notation, like this:
range myCol=col("Measurement Time");
myCol.type=4;
Basically, LabTalk object column can be accessed either using the wks.coln notation, or you define a range variable to refer to it.
Range variable allows you to refer to a column in any book sheet, like:
range AA=[book3]"Experiement A"!col("Start Time");
CP