Sanitize
Sanitizing is the reduction of microorganisms .....to a point considered not harmful to humans. It does not guarantee a kill rate of 100 percent, but rather to a minimum kill ratio of 99.9 percent.
Sterilize
Sterilization is the complete inactivation of all organisms: fungi, bacteria, viruses, and spores. Steam requires a minimum of 15 minutes at 250F or 3 minutes at 274F. Dry heat requires at least two hours at 320F
-Yeast the Practical Guide to Beer Fermentation, Chris White and Jamil Zainasheff
(and also many many other sources)
Wort does not need to be sterile as the items that survived sanitation will not be able to overcome the yeast after pitching. If you want to save UNFERMENTED wort, for say future starters, then that
does need to be sterile.
More on topic...
I cool while whirpooling through a counter flow chiller. After I've reached pitching temp (or as close as i can practically get during the summer) I let settle for 10 minutes and then transfer. On the occasional beers that require a hop stand I just turn off the cooling water and set the heating element to maintain at the stand temp (if it is a long enough stand). 30-60 minute Whirlpool as a standard practice seems excessive to me.
One time after a long day I was finishing a beer with 2-3 hop stands. During the last stand ~80-90F ish I forgot to turn the element off when the stand was over. I turned the cooling water back on and could not, absolutely not, understand why I couldn't cool the wort to below 80F when the single pass temp was in the 60Fs. After giving up and starting to transfer to the fermenter I figured out the issue very quickly when the wort level dropped below the heating element top.
Don't do that.