I just did a route calculation with Google Earth with their newly updated maps which include the construction at Kallang. It is only 8km, 2km shy of my original estimate of 10km.
Average timings for 10km races are about 57min to 58min. Although I must consider that the timings are of competitive canoeists in K1 kayaks using carbon wing paddles. I use a touring kayak and a heavy training canoe polo paddle, but would a change in equipment lead to covering an additional 2km distance within my usual timing?