If 10,000 people work one hour in one day, then that day still had 10,000 hours worked even if a day is only 24 hours.
Same with CPUs, many of them run on more than just one core.
I mean I had the programme running for 10 years, donating whenever it was on and idle or on a low load. It was not necessary to be perfectly idle, the programme could take just e.g. 50% of the CPU. (Famously on a core2duo running programmes that were not multi-core).
All in all my computer was probably on 12 hours per day