Eli Manning is on the clock.

No one knows how long he has, but when the Giants selected quarterback Davis Webb out of California with their third-round pick Friday night, choosing him 87th overall, they began the process of transitioning from one franchise quarterback to what they hope will be another.

“Let me get this straight,” general manager Jerry Reese said. “We’re hoping Eli plays for a long time for us. Eli is our quarterback and we think he can play at a very high level for a number of years. But we do know he’s not going to play forever.”

The last time the Giants picked a quarterback was Ryan Nassib, and when they made that selection, Reese said the ideal situation would be if he never played a snap. This time it’s different.

“We hope Eli continues to play at a high level and this guy can develop,” Reese said. “That’s what we hope for.”

The Giants had advertised their intentions to search for Manning’s heir this offseason. They added Geno Smith and re-signed Josh Johnson in free agency. But taking Webb with such a high draft pick — the highest pick they have used for the position since they maneuvered to take Manning in 2004 — certainly creates a lot more urgency in the room.

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And for Manning, 36, it’s the first true challenge to his role as the face of the team.

“He understands he is not going to play forever,” Reese said.

Reese said the Giants let Manning know of the selection.

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Manning, who has won two Super Bowls for the Giants and started 199 consecutive regular-season games, almost undoubtedly will be the starting quarterback in 2017.

He has three years remaining on his current contract. At that point he will be pushing 40, and while it is not unheard of for quarterbacks in this era to be productive at that point in their careers — look at Tom Brady — it seems as if the Giants have prepared themselves for the possibility of a change.

This pick was made with 2020 vision, as in looking toward the 2020 season.

“We think he’ll have time,” Reese said. “Obviously we’d like him to have a couple of years to play the caddie, but he has all the tools to play quarterback in this league.”

Even if Manning does continue to play for a good number of years to come, Webb can have value beyond the field. A quality quarterback can fetch a high price from passer-starved teams around draft time. If, in three years, the Giants still are comfortable with Manning, they could shop Webb around and pick up some extra picks.

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If they believe Manning is done, though, Webb might be there to step into the job.

Webb, a 6-5, 229-pounder, played three years at Texas Tech before transferring to Cal for one season. In 2016 he threw 37 touchdown passes and 12 interceptions. He has a live arm and is a pocket passer. “We thought he had the best arm in the draft this year,” Reese said. “We think this guy has a high ceiling. He can come in here and develop and create great competition at the quarterback position.”