It looks as though PyYAML interprets the string 10:01 as a duration in seconds:
import yaml
>>> yaml.load("time: 10:01")
{'time': 601}
The official documentation does not reflect that: PyYAML documentation
Any suggestion how to read 10:01 as a string?
Put it in quotes:
>>> import yaml
>>> yaml.load('time: "10:01"')
{'time': '10:01'}
This tells YAML that it is a literal string, and inhibits attempts to treat it as a numeric value.