I ran a sub-90 HM last fall as a time trial. It was my first attempt at the distance and I'd been running for 5 years. I definitely could not have run that time my first year or two as a runner. (But I'm a woman - a beginner man could more easily get there.) In the months leading up to my time trial, I ran 40-50 miles a week with one workout a week of half marathon pace miles (like 5-7mi continuous at 6:50 pace, or breaking it up into something like 3x2mi @ 6:50 pace with 1-2min rest) and sometimes a second workout of faster (5k-10k pace) stuff (Ks, 800s, miles). Later in the training cycle I incorporated HMP segments into a couple long runs (14-15mi total with up to 8mi interspersed in there at HMP) which were hard but gave me a lot of confidence.
I think my training here was rather unconventional and I wouldn't necessarily recommend doing the exact workouts that I did, but I had fun and achieved my sub-90 goal. I hope you stick with it and keep training even if it takes more time and attempts than expected to get that sub-90. It's a fun distance to train for.