A "red hot minute" is a very long time, ranging from two to three or more hours, or a few months to years in between the last time you seen someone or did something.
"Red hot minute" is longer than a "hot minute". A hot minute meaning you haven't seen or done something in a long time ranging from 20-30 minutes to an hour or more.
It's been a red hot minute since I last seen you.
When are you coming back through?
It'll be a red hot minute, but I'll be through.