When does Mr. Wickham meet Elizabeth in Pride and Prejudice?

They meet in Chapter 16 in Meryton.

But the attention of every lady was soon caught by a young man, whom
they had never seen before, of most gentlemanlike appearance, walking
with another officer on the other side of the way. The officer was
the very Mr. Denny concerning whose return from London Lydia came
to inquire, and he bowed as they passed. All were struck with the
stranger's air, all wondered who he could be; and Kitty and Lydia,
determined if possible to find out, led the way across the street, under
pretense of wanting something in an opposite shop, and fortunately
had just gained the pavement when the two gentlemen, turning back, had
reached the same spot. Mr. Denny addressed them directly, and entreated
permission to introduce his friend, Mr. Wickham, who had returned with
him the day before from town, and he was happy to say had accepted a
commission in their corps. This was exactly as it should be; for the
young man wanted only regimentals to make him completely charming.
His appearance was greatly in his favour; he had all the best part of
beauty, a fine countenance, a good figure, and very pleasing address.
The introduction was followed up on his side by a happy readiness
of conversation--a readiness at the same time perfectly correct and
unassuming; and the whole party were still standing and talking together
very agreeably, when the sound of horses drew their notice, and Darcy
and Bingley were seen riding down the street. On distinguishing the
ladies of the group, the two gentlemen came directly towards them, and
began the usual civilities. Bingley was the principal spokesman, and
Miss Bennet the principal object. He was then, he said, on his way to
Longbourn on purpose to inquire after her. Mr. Darcy corroborated
it with a bow, and was beginning to determine not to fix his eyes
on Elizabeth, when they were suddenly arrested by the sight of the
stranger, and Elizabeth happening to see the countenance of both as they
looked at each other, was all astonishment at the effect of the meeting.
Both changed colour, one looked white, the other red. Mr. Wickham,
after a few moments, touched his hat--a salutation which Mr. Darcy just
deigned to return. What could be the meaning of it? It was impossible to
imagine; it was impossible not to long to know.

In another minute, Mr. Bingley, but without seeming to have noticed what
passed, took leave and rode on with his friend.

Mr. Denny and Mr. Wickham walked with the young ladies to the door of
Mr. Phillip's house, and then made their bows, in spite of Miss Lydia's
pressing entreaties that they should come in, and even in spite of
Mrs. Phillips's throwing up the parlour window and loudly seconding the
invitation.