HOUSTON — Jakob Johnson received his playbook about 30 minutes before the Giants’ flight out of New Jersey was wheels up.

Twenty-five hours later, without the benefit of a single practice with his new team, Johnson was on the field for eight offensive snaps Saturday during the Giants’ 28-10 preseason loss to the Texans.

“I got a lot of practice cramming for exams in college,” the University of Tennessee product told The Post, “so I feel I used some of that to make this work.”

Besides, what is the call for clearing a path with a bone-jarring block?

That’s what fullbacks like Johnson are supposed to do — and exactly what he did in springing Eric Gray for a 13-yard run.

“You don’t need a playbook for that. You buckle up your chinstrap and hit somebody,” Johnson said. “It’s a blessing because you spend so much time preparing for a moment that might come, might not come.”

When he signed Friday — less than two weeks before cut day — the German-born Johnson was a stranger to most of his teammates and coaches. But not to all.

Like three newcomers to the Giants — right tackle Jermaine Eluemunor, right guard Greg Van Roten and offensive line coach Carmen Bricillo — Johnson was with the Raiders last season. Call it a Block Party.

Johnson dropped a pass when given a chance to touch the ball.

“I told the team to not get me a hotel room,” Johnson said. “I’m staying at Jermaine’s house. I know he’s got enough space over there.”

Familiarity is one of the reasons the Giants were considered Johnson’s likely free-agent destination dating back to Bricillo’s hiring. It took longer than expected.

“I thought that ship sailed just because we are so deep into [season] preparation,” Johnson said. “But you never know. That’s how this league goes.”

The Giants had been using Daniel Bellinger in a pseudo-fullback role as his share of tight-end snaps dwindled.

But Johnson brings 67 games of experience (34 starts) as part of two top-10-ranked rushing attacks with the Patriots and a key cog in Josh Jacobs’ 2022 NFL rushing title.

Johnson laughed that halfback Joshua Kelley at least snuck in one practice with the Giants after he signed Thursday.

He credited his offseason trainers in Florida for preparing him to “cut it loose” right away.

“They kept me on track, even in the weeks where I might’ve been like, ‘Hey, I don’t know if this call is ever going to come,’ ” Johnson said. “They made sure I’d show up to practice, stay in shape and be ready for when this call comes.

“Of course, I would’ve expected it to come with a little bit of practice in between, but when you get your opportunity, you have to make the most of it. You just put it on tape, and coaches make the decision off that.”

Head coach Brian Daboll received a strong recommendation on Johnson from former Patriots fullback James Develin.

“It’s not easy,” Daboll said of Johnson’s game-before-practice assignment. “We put in a few plays that he felt comfortable with, and that’s what we called.”