The large date is about 1/3 of a mm wider. It is also slightly taller. Will try to add a scan in a bit.
Scanned stamps are 3540a & 3540e. Small date is almost exactly 1mm ... large date is slightly wider. Probably less than 1/3 mm more ... maybe 1/4.
After an attempt to measure the difference, I think the width difference is no more than 0.1mm. The difference in height is easier to see.
