in no sense of the world should it be longer than 20 or 30 minutes
even track athletes who do interval training are only there 1 hour total from the time they get there, talk to coaches, train and talk to coaches and go home
this absurdity you see on social media of guys claiming they train hours a day is just that ABSURDITY. there is zero benefit to pounding your body into the dirt. pro athletes don't train that much for crying out loud
for the record i am not an advocate for HIIT or interval training anyway, it causes more harm than good. great way to get injuries