Don't feel guilty, think about the purpose of the workout. If it's a fartlek, where you are trying to build fatigue and still hit a pace when fatigued, then you need to jog or float the rests. If it's an interval, where you are trying to hit a pace that is quite fast, then walk the rests. it's all about meeting the purpose of your workout. It took me a long time to get that through my head. I don't have a garmin so can't show you exactly, but here's a link to a video on how to set up the workouts: kzfaq.info/get/bejne/fs1-gbWf26vFZ3U.html

I’m just training for the half at the moment. I’ve never been under 90 minutes so I’d like to knock that milestone off in Cairns if I can.

Best of luck with it. I definitely reckon you can do it