Daily commute as HIIT training?
8 km is very short to be able to get in a quality warm-up and cool-down while still having time to get any decent intervals in. Unless you're a complete beginner, you're unlikely to get any meaningful benefit from doing intervals rather than just riding to work steadily. VO2 max intervals tend to be 4-10 minutes each, usually at least 4 in a session with very short ready intervals in between. This is because the most important factor for VO2 gains is the amount of time spent oxygen-depleted.

The only thing that I could see you improving during such a short ride would be your sprint. If you add in some very short (10-15 seconds) max efforts you may find that your peak power improves and the muscular improvement does somewhat help you in your longer rides. For your first few, do them on an uphill section (doesn't need to be very steep) and slow right down to nearly a stop. You should be in a gear that feels much too heavy when you start, but by the end of the interval your acceleration should have you spinning it at a reasonable cadence. These are more of a strength workout than a cardio workout, so you may find that you end up spending almost your entire ride recovering from the short intervals. Just remember that if you don't feel almost broken by the end of the session, you aren't doing proper strength work. Doing these twice a day, five days a week will eventually put far too much stress for your body to recover in time to do a quality session next time. Start off doing it once or twice a week, then maybe ramp up to three once you're used to it.