Minutes per session

Hi. Im new to triathlon training and just trying to get the consistency down with the amount of training per week. Ive been lifting and running for several years, but I am new to biking and swimming. Not sure why its taken me so long because Im really enjoying it!

Anyway, I printed out the balanced Olympic training plan due to my current fitness level and I understand the 10% rule for increasing volume. But since its so exact, I feel I might be too concerned with the minutes and not just finishing the mile or swim meters. For example a 21 min run. What if Im at 1.78 miles or 2.3 miles, do I just stop? Same goes for the bike ride and swim. Do I set a timer on my phone so Im not distracted by constantly checking the time?I have been swimming and even number of meters per week and the time changes a little each week depending on how I feel, but its the same amount of meters like 1500m not 1425.

Just thought I would ask so I can understand the program and have confidence moving forward. At the moment Im not signed up for a race, Im just picking a week that fits my fitness level so I can stay consistent, work on my form with swimming and getting time on the saddle. Eww it hurts. lol

Thank you