So I thought I'd share my thoughts as well.
Lessons Learned
First, the "heroic rest" did not work out. I was trying to go for an adventure where there was such a time crunch that you wouldn't really be able to rest, but in reality there were a few times you could have taken a short rest like normal, like after the boat and after the dragon fight. There wasn't a long rest as by midnight you could still fight Hythonia but the king's daughter would have been a gorgon. Maybe I could have given you a choice to take a long rest, but I didn't think any of you would want to lose at half of the quest.
Second, the legendary resistance was meh. Probably not enough spellcasters to really test, but overall probably sticking with the old system would have worked better.
Lastly, i'm not sure how I felt about the potions i gave hythonia, but I greatly regret the potion of flying. Not sure why I felt the need to use it. I think the potion of heroism and the potion of giant strength were enough, if even too much.
I had originally planned to have a skill challenge to get the boat to the island through the rocky shore, but was bewildered when the party didn't want to bring the boat to shore at all and as such what I thought was going to be cinematic was instead avoided by player choice. This was not on the players, but instead on me for having a solution in mind instead of having a problem and letting the players do as they wished. As such, make future one-shots more open ended to see what the players come up with rather than assuming "players must do x at this location".