Yep, I'm in the same boat. Only swum once or twice this year, and in for the 5km. Done it for the last couple of years, so know what I'm in for. I can only manage two sessions per week, one will be about 1:10, and be generally 40 to 50 100's, then another 0:30+ which will be drills etc. It aint going to be pretty, but hey ho!