Sometimes it is good to have a sense of what is considered "normal" for an event. One of these of interest to calf rearing persons in the healing rate of the umbilical cord among newborn dairy calves. 
Observations were made during an evaluation of four different compounds used for navel dipping. The umbilical cord diameter was assessed within 30 minutes after birth and again at 24 hours of age. [Robinson, A. L., L.L. Timms, K.J. Stalder and H.D. Tyler, " The effect of 4 antiseptic compounds on umbilical cord healing and infection rates in the first 24  hours in dairy calves from a commercial herd." Journal of Dairy Science 98:5726-5728 September 2015]. Sixty calves were observed.
Average umbilical cord diameter was 0.9 inches (22.8mm). Most calves fell in the range of 0.75 and 1.05 inches.
24 hours
Average umbilical cord diameter was 0.3 inches (7.6mm). Most calves fell in the range of 0.14 and 0.46 inches.
Normal healing rate (shrinking diameter)
From 0.9" at birth to 0.3" at 24 hours. 
Outlying cases that I would tag for watching
1. Diameter well over 1" at birth.
2. Diameter remains over 0.5" at 24 hours.
By the way, always remember to train and retrain all the folks doing the navel dipping to:
1. Dip umbilical cords soon after birth.
2. Use clean dip and a dip container.
3. Expose the entire umbilical cord to the dip.
4. If the dam has removed all the dip, re-dip the navel after removing the calf from the dam.
BTW you might be interested in the dollars and cents of navel dipping at this resource sheet: click HERE.