I'm so interested to see the responses to this question! We do let our kids stay up later than normal during school breaks, and sleep late in the mornings. But, for the final 2-3 nights of the break, we get them to bed at their normal time and wake them up early so the transition isn't as hard when school starts again.
My kids will stay up later when they have a school break or holiday, however if we have something special planned for the holiday and still need to leave the house early, I try to get them to bed at the same time. But most school holidays, I will work from home/or a venue with WiFi and take care of the kids so we aren't in a huge rush to leave the house in the morning.
I let them stay up a little late during school vacations if I'm off from work and we don't have anywhere to be. My older boy typically is up at 6 am no matter what time he goes to bed so letting him stay up often backfires for me.