How would you split an athletes time over the three disciplines, S&C and stretching?
This one definitely depends on your target event distances/disciplines and your personal relative strengths/weaknesses, as well as injury history in relation to S&C/mobility work needed.
As a rule of thumb, for an age-group triathlete competing in sprint and standard distance events, I would look at two S&C/mobility sessions of 30-60min per week, then remaining training hours would split approximately 25% swim, 50% bike, 25% run.
Long-distance triathletes might shift a little extra emphasis from swim to bike compared to that model, whereas for athletes competing in draft-legal events it would go the other direction as the swim is so crucial in terms of making the fastest possible bike group.
For youth and junior triathletes targeting British Super Series racing, the balance would shift almost in reverse, with the swim and run making up the majority of the programme as the technical demands of these disciplines are crucial to develop at the younger ages.