"It has been a long time since we last met."

"It's been a long time since we last met."

Perhaps, "It's been one week since you looked at me..."?

It's common for en_GB, I can't speak for en_US though. Here[0] is a test with it used twice.

[0] http://www.bristol.ac.uk/arts/exercises/grammar/grammar_tuto...

"It's" for "it has" is much more common in spoken English than written (even moreso than is explained by the fact that contractions are generally avoided in formal writing.)

But it is a real thing.