My first extension of stay based on marriage expires early next month. 

 

I was informed that I can apply to renew it within the last 30 days of its validity. 

Can the renewal application be submitted at any time during the last 30 days of validity i.e. within the last 2 weeks?

Or do I need to actually apply for it 30 days before the first one expires?

You can apply at any time during the last 30 days of your current extension up to the last day.

My last application for marriage extension was presented 6 days prior to the previous one expiring. No problem at all.

Great - thanks to you both for the replies. I don't intend to leave it particularly late but good to know that it doesn't have to be done right away