I used a quick mapping program to check, but the distances seemed pretty accurate. It's about 2 miles from Akershus, around the world showcase, through the international gateway, and then following the path to DHS (by way of the Boardwalk). Without kids, I could make it in half an hour, give or take, depending on crowds and how much of a hurry I was in.
In general, if I cannot see the boat coming when I am at the International Gateway, I can walk it faster than the boat will get there, unload, load and get to DHS. That's without kids though - a stroller slows me down a little, and if they are walking, it could take a lot longer.