How do you lengthen the amount of time that Time Machine keeps hourly backups?
The answer is this isn't easily done. Apple doesn't expose the timing which means it's likely to change if you apply any updates to the system or the change might even break backups so they don't run.

I've left a comment asking about the use case. I've employed scripts to get around this in several cases for customers, but I'd need to know more about your actual use case before providing an alternate solution that would work even with the default Time Machine scheduling.