Thanks, Ludkeh, appreciate the comments. The races around here are all in the 20km range (13 miles, plus/minus), so pretty short by the standards of this board.
After sifting through lots of material, and figuring out what is actually reasonable in terms of time, I've settled on a three sessions a week focused on cycling training. One for endurance/aerobic, where I do 1.5x-2.0x the distance as fast as I can, one for intervals, which has set times, but no set distances, and one for "recovery", which is moderate effort and about 0.75x race distance.
I know folks say you can hammer out 5 days a week cycling because it's relatively low impact compared to running, but I also have two sessions of weight lifting/swimming and three ~45 minutes runs a week, and that's about "all" I can afford.
Anyway, will stick to this plan for a month, and then re-evaluate.