HIIT for 20 minutes is a bit insane. For those who don't know its basic concepts are you pushing your heart rate to maximum for a set amount of time, then coming to a moderate heart rate, and pushing back to max repeatedly. If you've trained before your maximum heart rate is not the standard 220-(your age), so you will have to measure it out with a heart rate monitor.

Also, your 'rest' period may be interpreted incorrectly. You should be coming to a jog (if running). Like max speed for 30 secs, jog for 15 secs, MAX for 30, rinse and repeat. Most HIIT sessions don't last 20 minutes unless there is a 5 min jog warm-up and cool down. Push the times up slowly. 20 secs is a good place to start with 10 sec 'rest', but aim to slowly increase. When I started, each week I added 2 secs to sprinting hard, 1 sec to rest. Now when I do it, I typically do 60 sec Max, 30 sec rest, 10 sets, fifteen minutes and a gallon of water later I am finished.

For HIIT, I do recommend a timer, GymBoss. No spam here, best $20 I've spent for a workout piece EVER.

As for long runs, I avoid them most of the time personally, maybe do it once a month now. I have lost the need to be able to run 6-10 miles so I don't train it. Back when I did soccer super competitively, either early morn, at least 5 hours before lifting, or any time after lifting.