Bellkrank

so im fluching my cooling system with the PEAK super cleaner/flush and after the 1st flush it telly you to then add cleaner and water and "drive" for 3-6 hours for best results. well im i did this all at work and know i have to work all night.
will the cleaner be OK in the system for over 12 hours? i dont want it to start eating away at my rad and core...

I think im just overthinking simple directions