After becoming the first NBA team to reach the halfway point in the schedule, the Celtics suddenly have lots of time to stretch out, practice and get a massage.

But no one needed this break — tomorrow’s date against the Philadelphia 76ers at O2 Arena as part of the NBA Global Games will be the C’s only game in a nine-day stretch — more than Al Horford.

“Definitely different for us,” Marcus Smart said. “We’re used to playing three and sometimes four games a week. This rest is much-needed. You see Al over there with the ice on his knees.”

Indeed, Horford still doesn’t know why his left knee suddenly developed soreness last week, leading to his absence during Saturday night’s road win against the Brooklyn Nets. But thanks to this week’s prolonged rest period, he expects to play tomorrow.

Horford ran through a full practice yesterday when the team worked out at a small health club.