BikeCAD provides all sorts of information about tube lengths. Center to center tube lengths are found in the Frame tab of the Dimensions dialog box. These dimensions are listed with the abbreviation (c-c). The top tube center to center measurement goes from the center of the seat tube - top tube intersection to the center of the top tube - head tube intersection.
The Mitering tab contains various dimensions listed as miter to miter lengths. For example, the miter to miter distance along the top of the top tube, measures the distance between the inner edge of the miter at the rear to the inner edge of the miter at the front. If the seat tube and the top tube are not parallel, or if the head tube is tapered then the miter to miter distance along the top of the tube will be slightly different than the miter to miter distance along the bottom of the tube.
New for BikeCAD version 13.5 is the option to show minimum tube length. You'll find the minimum top tube length under Tubing - Top tube. The minimum tube length is the distance from the tip of the tube in the rear to the tip of the tube in the front.