This. 90 minutes is by far the optimal time for training distances half marathon and under. If you’re worried about time then your half marathon is likely 2 hours or under and it is not a big deal if your longest run doesn’t equal that so long as you’re getting in good consistent mileage across the week. People have mentioned Jakob not doing more than 12 miles in a long run as a counter example and that’s great; how does your body respond to long runs in regards to the other runs of the week?
ideally you’re getting in VO2max targeted workouts, thresholds, and workouts targeting lactate threshold etc. So if your long run is leaving you too wiped out to knock those out effectively, it’s the first thing to reduce. The advantages over one training cycle are not large enough to justify the diminishing returns. Lower impact on the body (grass or treadmill) can compensate for the wear and tear but you can google around for studies that show the decreasing utility for runs above 90 minutes versus increased injury risk.
You can basically ignore anyone’s answer that just talks about amount of miles. Time on your feet is a better metric that accounts better for whatever pace you’re running anyways. Long runs I won’t discount as good training but personally they didn’t work well for me, left my body feeling terrible anytime I went above 12 miles, and so I dropped them and substituted them with 8.5-11 mile runs on the treadmill at slightly slower than marathon pace.
Worked wonders, I got the turnover I needed and the cardio, and my track workouts quickly improved, and led to knocking down a 70 min half and 2:28 full in the same season. Definitely not pro times and almost certainly not the best regiment I could’ve done but just want to illustrate there are others ways and you need to test out what your body responds to best with the time and facilities you’ve got around you.