Nowt wrong with S/B/R only! I failed to mention hamstring stretches and shoulder mobilisation stretches, but these take up minimum time.
I've thrown some numbers together - if I'd swum for 3 hours per week for the last 10 weeks rather than 2, my percentages would not have differed too much (+3% on swim, -1% on bike and -2% on run). I guess my numbers were slightly skewed anyhow as I didn't swim in Feb/Mar due to a shoulder injury.