For as long as most New Yorkers can remember, the rules have been clear: Enjoy Central Park by day. Keep out at night.

Someone, however, forgot to tell Fleur Bailey, a petite Wall Street trader who was walking her two Dalmatians in the park after 10 the other night.

“I can’t remember the last time I came across something that made me uncomfortable,” said Ms. Bailey, who lives on the Upper West Side and takes her dogs into the park as late as midnight. “Some people say, ‘You walk your dogs where at night?’ But I tell them that it’s perfectly fine.”

And she is hardly alone. On any given evening, the park now hums with life well into the night. Couples stroll under pools of lamplight, while the park drive pulses with the footfalls of runners, the whir of cyclists and the desultory clop of carriage horses. Men and women jog happily around the reservoir.