Can it be abbreviated as it's?

It cannot be abbreviated as it's. Be's past tense was, were can't be abbreviated generally, because it will cause tense confusion. For example:

Yesterday was National Day.

Yesterday was National Day. (cannot be abbreviated as was)

She was very sad last night.

Extended data:

Sometimes it means it is, sometimes it means it has, but it doesn't mean it is. For example:

It's very cold today. ?

It's very cold today. (it's = it is because this is a system table structure, so it is today)

Arrived early today. ?

Arrived early today. (it ' s = it have； Because arrived is an intransitive verb)

It is made of wood. It is made of wood. (it's = it is, forming a passive voice with made)