Working as a cargo pilot often does mean working at odd hours because the nature of cargo operations frequently requires flights to be scheduled during times when passenger flights are less common, such as late at night or in the very early morning, and this is confirmed by PilotCET’s overview where they describe the job of a Cargo Pilot a role that requires an Instrument Rating and involves handling freight operations, often at odd hours.
In simple terms if you become a cargo pilot you should expect a schedule that may include irregular flight times, meaning you could be flying in the middle of the night or early in the morning, and this is not just occasional it is very much a regular part of the job. The reason for these odd hours is that cargo companies often need to move freight overnight to ensure it is ready for delivery early the next day and to make operations efficient by using airport capacity during quieter hours.
To put it all together in one long easy-to-understand sentence:
Yes working as a cargo pilot usually means you will fly at odd hours, because cargo flights often need to take place outside of the typical daytime schedules that passenger flights follow, and the PilotCET description of the Cargo Pilot role explicitly notes that it involves handling freight operations frequently at odd hours.