Oliver Cowdery says he met JS for the first time on April 5, 1829.

Date: Sep 7, 1834
Type: Letter
Source: Oliver Cowdery
LDS
Hearsay: Direct
Reference: Oliver Cowdery, Letter to William W. Phelps, September 7, 1834, rep. Messenger and Advocate 1, no. 1 (October 1835): 14
Scribe/Publisher: Oliver Cowdery
People: Joseph Smith, Jr., Oliver Cowdery
Audience: W. W. Phelps, Reading Public
Transcription: Near the time of the setting of the Sun, Sabbath evening, April 5th, 1829, my natural eyes, for the first time beheld this brother. He then resided in Harmony, Susquehanna county Penn. On Monday the 6th, I assisted him in arranging some business of a temporal nature, and on Tuesday the 7th, commenced to write the book of Mormon.
Source Link: https://contentdm.lib.byu.edu/digital/collection/NCMP1820-1846/id/7012
Citations in Mormonr Qnas: The Book of Mormon and View of the Hebrews