ok its confirmed. You really dont have to continue to save and load, just stop staying in the same spot. If your on the platinum strips and youve mowed down the zombies there, just go to the silver strips and theyll be repopulated. Rise and repeat with your 25k kill bike.
I restarted to use the ike and im at day2 2pm with 33k kills and saved but have not reloaded a single time.