From 0:00-3:00, perform 3 rounds of:

• 3 pull-ups
• 6 push-ups
• 9 squats

From 3:00-6:00, perform 3 rounds of:

• 4 pull-ups
• 8 push-ups
• 12 squats

From 6:00-9:00, perform 3 rounds of:

• 5 pull-ups
• 10 push-ups
• 15 squats

From 9:00-12:00, perform 3 rounds of:

• 6 pull-ups
• 12 push-ups
• 18 squats

Etc.

Continue for as long as possible until you cannot complete 3 rounds within the 3-minute window. Every 3 minutes add 1 additional pull-up, 2 additional push-ups and 3 additional squats.