Save the sprinting for the last 3 weeks. 30 minutes of walking wont win him a trophy. You're at your 3rd week already, he should be walking or trotting on the mill for 8-12 hours building up his legs for the strength work and cardio at the end of his keep. Walk him more, twice a day if you have to. Gotta get them hours in bro. That's how you win.