How long is the orientation year permit valid and can it be extended?

The orientation year permit gives you exactly one year of residence to search for and start work. It cannot be renewed, so it is genuinely a single window rather than a status you can keep extending.

What you can do is move on to a different permit before or when it ends, for example a highly skilled migrant permit, a start-up permit, or a self-employed permit, provided you meet that permit's conditions. Many people treat the orientation year as a launch pad into one of these longer-term routes.