"Nice to meet you" and "Nice meeting you"

[Fredenglish]

Hello,

How should the followings be used in a conversation? "Nice to meet you." "Nice meeting you."

Thank you in advance

 

[emsr2d2]

Nick: Hi. I'm Nick.
John: Hi. I'm John. It's nice to meet you.

Later ...

Nick: It's time for me to go, John.
John: OK. It was nice to meet you/It was nice meeting you.