5. (5 points) The time it takes for $A, B, C$ to complete a project individually is shown in Figure 1. If $A$ starts working at 8:00 AM, and 27 minutes later, $B$ and $C$ join, the three of them work together, then the time they complete the project is $\qquad$ minutes.
Solution: According to the problem, the efficiency of $A$ is $\frac{1}{6}$, $B$'s efficiency is $\frac{1}{4}$, and $C$'s efficiency is $\frac{1}{5}$,
$A$ works for 27 minutes, which is converted to hours as $\frac{27}{60}=\frac{9}{20}$,
The work done by $A$ is $\frac{1}{6} \times \frac{9}{20}=\frac{3}{40}$,
The remaining work is $1-\frac{3}{40}=\frac{37}{40}$,
The combined efficiency of the three people is $\frac{1}{6}+\frac{1}{5}+\frac{1}{4}=\frac{37}{60}$,
The working time is: $\frac{37}{40} \div \frac{37}{60}=1.5$ (hours),
Adding 1.5 hours to 8:27 is 9:57.
Therefore, the answer is: 9:57.