Adding hops into hot wort post-boil is called a “hop stand.” The other term you’ll hear is “whirlpool hops.” 10-20 minutes in 70 C wort is a great way to get a lot of hop aroma without much bitterness. And you don’t have the oxygen exposure issues that can come with dry hopping. It’s a great technique for beginners, and for that matter, experts.
You generally don’t want your wort to sit for too long at 80 C or above because you'll create DMS (dimethyl sulfide) that then won’t get driven off, and your beer will taste like canned corn. That will be a bigger or smaller problem, depending on the style of beer and the sensitivity of the people drinking it.