Synchronized sources

1. If they matched at 12:00, the next triple match is at 12:36.
2. Since that triple match occurred 20 minutes after entering: $12{:}36-20\,\text{min}=12{:}16$.
3. Match check from exactly two sources from 12:16: at 2 min: 12:18 (6 and 9 match).

Back to problem
Answer: came in at 12:16.
The three sources each agree:

$$ \operatorname{mcm}(4,6,9)=36\ \text{minutos}. $$

If they matched at 12:00, the next triple match is at 12:36.
Since that triple match happened 20 minutes after entering:

$$ 12{:}36-20\ \text{min} = 12{:}16. $$

Match checking from exactly two sources as of 12:16:

• at 2 min: 12:18 (6 and 9 coincide),
• at 8 min: 12:24 (4 and 6 coincide),
• at 20 min: 12:36 (3 o'clock coincide).