When was a lamb allowed to be sacrificed as the Passover lamb?

Les teaches that the lamb was to be brought up and pinned up until the 14th, which would be three full days. During that time they were to examine the lamb every day to make sure there was no blemish. If there was the slightest thing wrong with it, they had to reject it for being their Passover lamb. But if after those three days of scrutiny they were satisfied it was perfect, without blemish, then they could offer it as their Passover lamb. Les explains the picture: those three days were comparable to Christ's three years of earthly ministry, where He also proved Himself without blemish. As Paul says, He who knew no sin never sinned. His three years was impeccable, and He proved Himself worthy to be the Passover lamb—a lamb without blemish and without spot. Les then directs attention to Hebrews chapter 9, verse 22, emphasizing the blood regardless of what liberals may say or remove from hymn books.