The system date time token will work without you needing to do anything - they'll just populate with what the date & time was when the smart campaign runs.
It is possible to create a my.system datetime token in the sense that you can create a token by that name. But my tokens (program tokens) require you to populate the value or create velocity script to run it - can't think of any use case where you'd need to do that rather than just using the system token.
Program tokens are great for things that are more specific to your brand, or (for velocity scripting) when you want to do things that are specific to each lead. I often use program tokens for ctas, utms, program templates, etc.