I did a nice balls set of HIIT today, and I can already feel my calved/thighs are tight as hell, and I'm going to be sore as a popped hymen in the morning.
Should I do it again tomorrow, or should I wait? How will I know when I'm ready for more?
It depends when you train legs. If you havent trained legs this week Id do low intensity cardio to get some blood flow and aid recovery. If you have done legs this week then get after it on the track again.