Good to know thanks.
EDIT: I think there's a lower chance of gaining skill when you have a higher skill level. Tybilt has 60 or 65% swordsmanship now and it's mostly been expensive failures to increase it. Even when I used the full 6 hours twice today. It's a expensive and disappointing, but seems pretty realistic.
Well I always thought the higher you get, the lower your chances.. But that's just me thinking out loud.
In my experience, I never use multiple 3/4 hour windows. Always full hours.