launchctl list doesn't show StartInterval
StartInterval won't get printed with (sudo) launchctl list [label].

Use sudo launchctl print system/[service-name] instead. It will be printed as run interval.

Depending on the domain/service target use 


user/&lt;uid&gt;/[service-name]
login/&lt;asid&gt;/[service-name]
gui/&lt;uid&gt;/[service-name]


instead of system/[service-name]

Examples: 

host:~ user$ sudo launchctl print system/com.apple.collabd.expire | grep interval
    run interval = 600 seconds
host:~ user$ launchctl print gui/501/usr.homebrew.mxcl.autoupdate | grep interval
    run interval = 7200 seconds