Part of the charm of math boxes is that you can do a big expression in one shot, so you could do "MATH D4 (D0 * 60000) + (D1 * 1000)" and cut several rungs. I'd probably have them enter a single number like 5915, and split it into minutes and seconds in Do-More before doing the multiplying. For display, convert it into a string and insert the colon.