my non-o visa expires on 26 of oktober,when do I have to apply for a one year extension?

In the last month before the expiry date .

But don't wait until the last moment , 3-4 weeks before expiry is OK .

thanks,so at latest on friday 3 oktober(26 okt is a sunday)

Later still possible , but immigration prefers it stated above .

my non-o visa expires on 26 of oktober,when do I have to apply for a one year extension?

The expiration date of your non-O visa does not count, but the expiration of your permission to stay, ie the “until” date on your entry stamp. You should make your application for extension of stay any time during the last 30 days before the expiration of your permission to stay.

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Maestro