"Once in a lifetime" means to cherish the encounter that happens only once in one's lifetime.

He missed a once-in-a-lifetime opportunity.

I couldn't get in touch with her for a week.

We will meet again in one month.

My birthday is in November.

Sanichi is my best friend.

There was not a speck of dirt on his shirt.

This is the agenda for the first meeting.

He has a pencil.

He tried to solve the problem all night.