Yepp you are spot on about this !!!
See Modified column was just an example for you, you can basically create a custom column, fill it up with a date say 15th September 2020 and then just leave the flow was is.
Flow will trigger everyday and check if the date in custom column matches the current date till 14th September but on 15th September when your flow runs the condition will get matched and your flow will automatically be copied.
You can replace the Modified column with any column where you can push the date, important thing is that you now know the logic so you can create similar stuff for different scenarios.
Also, it would be great to accept my answer as a solution, if you think the answer has helped you and can be helpful to others looking for a solution to similar problem.