Last fall - beginning of 10th month - I was on Krn, started from Planina Kuhinja and it was quite ok early autumn day trip, undemanding, only fog welcomed me on top and just few seconds through hole saw Krn lake from other side. Otherwise path from Lepena personally much nicer, but this shorter.
Yesterday again headed to Krn from Planina Kuhinja, considering distance to start point (3.5 hours drive), arrived to start bit before 9:00. Although guide writes this side in summer extremely demanding due to sun, still went to top. Can say from personal experience really don't recommend such late start at these temps, as up to 1600 m a.s.l. completely exhausted. Literally grass was shining, and when inhaling felt like someone with hairdryer blowing hot air into mouth and nose. After 1600 m a.s.l. temp quite decent, but then already fairly worn out. On top was wonderful view, in my opinion from Krn one of nicest in Slo.
Overall, bit less than 3
hours up, bit less than 1.5 down, break on top 15 min. All together 4.5 hours walk, but exhausted as if walked 12 hours.
Think Krn next time in autumn or with sleep in hut and start at 5:00.