Wikipedia, incidentally, seems to support the shorter timeline:
“The official start of construction took place on March 8, 1942, after hundreds of pieces of construction equipment were moved on priority trains by the Northern Alberta Railways to the northeastern part of British Columbia near Mile 0 at Dawson Creek. Construction accelerated through the spring as the winter weather faded away and crews were able to work from both the northern and southern ends; they were spurred on after reports of the Japanese invasion of Kiska Island and Attu Island in the Aleutians. During construction the road was nicknamed the "oil can highway" by the work crews due to the large number of discarded oil cans and fuel drums that marked the road's progress.[9] On September 24, 1942, crews from both directions met at Mile 588 at what became named Contact Creek,[10] at the British Columbia-Yukon border at the 60th parallel; the entire route was completed October 28, 1942, with the northern linkup at Mile 1202, Beaver Creek, and the highway was dedicated on November 20, 1942, at Soldier's Summit.”