I've been seeing my fiance for 4 years now, and I came in to the relationship with 2 boys. My boys are now 12 and 9. Once a year me and the boys go to my family's vacation home with the entire family, and up until this year, my fiance did not attend.
But now that we are engaged and merging families, the family asked that he come too (they all get along great with him anyways). I explained to him prior to us coming to our family retreat that during our week stay with the family, my kids do not have a bedtime.
We do a lot of night activities, such as night swimming in the pool, karaoke, fires, nightly strolls through the neighborhood, etc etc. So during this week, my kids absolutely do not have a bedtime and this is how it has always been.
I made it clear that bedtime was not to be enforced like it was at home because this is vacation and time with family and I'm not making my kids miss out on the nightly activities. I also explained that due to this, some nights they are up until easily 11-midnight. It's once a year, it's no big deal.