This whole traverse was 7.5 miles (About 0.6 miles across Jim Lake, 3.5 miles down Jim Creek, and the rest is Knik River) and took about 4 hours beginning to the Old Glenn Highway Bridge (first bridge crossing), and driving time in between is about 25 for car staging. It would work as a bike-packing solo adventure as well, and would likely only take about an hour to bike out to Jim Lake from the Old Glenn Highway Bridge over Knik River.
If you want to keep going, Jim Lake to the Glenn Highway Bridge is 16 miles, and takes another 2 hours of floating time.
We started from Jim Lake parking lot, which is at the end of Maud Road, past the shooting range. From this location, we aimed a little too far to the right side of the Lake, found a portage to Jim Creek that worked, but after bushwhacking for 100 or so feet and floating Jim Creek for about 1/4th mile, we learned there was another, better route.
This was our slight bushwhack portage looking back from Jim Creek on my packraft. The paddleboarders decided it was best to leave their large fins on, despite the risk of grounding out. There aren't any rocks on this whole route, just sand, and if you do scrape up against the silt, you don't have far to fall.
This was the way we SHOULD have gone! From the parking lot, aim slightly left of Pioneer Peak, directly across from Jim Lake, and eventually you'll find a portage that is a lot easier to traverse than our bushwhack.
At the end of Jim Creek, where it intersects another stream. With about 1.5 miles to go until we hit the Knik River.
This was the point where Jim Creek intersected the four wheeler trails out to Knik Glacier. It got REALLY shallow, to the point where we had to get out and walk our floaty things about 200 feet.
Out on the Knik River, moving fast, but feeling like we were hardly moving.