And when he saw [them], he said unto them, Go shew yourselves unto the priests. And it came to pass, that, as they went, they were cleansed.
Note 1 at Lu 17:14: Notice that in the first healing Jesus ever performed on a leper (Mt 8:1-4, Mr 1:40-45, and Lu 5:12-15), He also told that man to go and show himself to the priest. This, of course, was to fulfill the scriptural requirement of Le 14:2 and grant the leper reentry into society. But Jesus also added, in His statements, to that man that He wanted him to go see the priest for a testimony unto them. Surely, that was part of His reason for sending these ten lepers to the priests also.
Note 2 at Lu 17:14: This verse makes it clear that these lepers were cleansed "as they went." They were not healed immediately but as they were on their way to see the priests. These men would have looked like fools when they presented themselves to the priests for the rituals of cleansing if their leprosy was not gone. This was a great step of faith for them (see note 4 at Joh 5:8 and note 3 at Mt 12:13).
Note 3 at Lu 17:14: This was possibly the longest amount of time recorded in Scripture that it took for anyone to whom Jesus ministered to receive complete healing. As explained in note 5 at Lu 5:25, most of the healings that Jesus administered were instantaneous. There is only one other example in Scripture where a healing came gradually (Mr 8:23-25).
In this instance, the amount of time that elapsed before the lepers' healing was evident is not given exactly. It could have been anywhere from a couple of minutes to an hour or two, but there was a lapse of time between when Jesus told them to go show themselves to the priests and when they saw that they were healed. Although this does establish a biblical precedent that not every healing has to be visible instantly, it should be understood that this instance and Mr 8:23-25 are the only two exceptions to instantaneous healings in the recorded ministry of Jesus.