The other night, while leaving a benefit at the Plaza, my husband and I bumped into an acquaintance we hadn’t seen in a long time. It was 10 p.m., and there was such a mass exodus from the dinner that it reminded me of Cinderella’s mad dash to heed her fairy godmother’s warning that at the stroke of midnight, all would return to the way it was.

As we left the Grand Ballroom (which, incidentally, looks exactly the same as it did before hundreds of millions of dollars were poured into the hotel), David and I couldn’t miss this friend, as he was lugging an enormous Lands’ End tote filled with work.

“Are you really going to go home tonight and go through that bag?” I asked skeptically. We were in an elevator full of folks like ourselves — married with children — all of whom looked like we might collapse on the floor from exhaustion.

“I always go home and do work,” he said. “But I used to be able to count on the kids being asleep from 10 p.m. to 1 a.m. Not anymore,” he said wistfully. His eldest child is 15 years old, and like so many of my friends with teenage children, he now calls it a day long before his children do.

For the first few years of raising children, parents look forward to the blessed hour when the gang is asleep. For some, this happens at 7 p.m. For others, it’s 9 p.m. But for nearly all of us with young children, there is a child-free hour or two at the end of the day to finish up e-mails, return calls, watch television, or have a peaceful meal or conversation.

Plenty of parents use this time to get a leg up on tomorrow’s workload. “There’s never a moment of peace at the office,” a lawyer and mother of two said. “Sometimes, I need that time after the kids are asleep to catch up on administrative details. Sometimes, I need it to take a close look at important documents.”

“At six o’clock, I begin the countdown,” a mother of four children under the age of 7 told me. “Two hours left until lights out. Thank god. Often, my husband and I will go grab sushi or see a movie, and the kids won’t even know that we went out.”

Sounds ideal. But then, almost overnight, the tables turn when children become teenagers.

“We’ll go out for a fun dinner, I’ll relax, have a drink or two, and then come home and guess who’s awake?” a mother of three teenagers asked me, illustrating her point. “Everyone! If we come home at 11 p.m. on a Saturday night, they’re all up. Our oldest, at 17, is out with friends. But the 13- and 15-year-olds, they’re home. Sometimes, they’re just hanging out in their rooms, listening to music or talking on the phone. A lot of the time they want to chat. Too bad if I have other things on my mind.”

Another friend with teenagers is a little more blunt about this new situation. “The only thing worse than having your 5-year-old walk in on you while you’re having sex is having your 15-year-old walk in on you,” she said. “That is what I live in fear of. I dream of the days when my kids used to cling to my legs when we went out at night. No matter how hard it was to get out the door, everyone was always sleeping when we came home.”

One mother of a 15- and a 17-year-old said that she’s exhausted because she doesn’t like going to bed when her children are awake. “For some reason, I really can only sleep well if I know the boys have gone to sleep. I can hardly tell my high school junior that he has to go to sleep when he tells me he’s studying for some important exam. But at midnight, I’m exhausted. My husband thinks I’m crazy. He’s always gone before me, and now is no different.”

Another mother of two teenagers, a doctor, said that a few years ago, she learned to let go of the evening hours. “I can’t dictate what the kids do after dinner and how late they stay up,” she said. “If I need to get some paperwork done, I try to do it. If we need to go out, we go out. Both of us try to be around for the kids, but not in their faces. When they want to let off steam at midnight, I want to be there to hear them. Sometimes, I make it that late; sometimes not.”

sarasberman@aol.com