Closing time frame on vacant neglected property

[Keith Ransom]

Hello 

I was wondering what most investors use for the time frame of due diligence and closing when submitting offers.

I recently submitted an offer on a vacant and neglected 30 unit  property where the owner owed 145,000 in back taxes.

I put in my offer 30 days due diligence and 30 days after to close.

The owner countered with 

Due Diligence: 15 Business Days

Close date with 10 business days after due diligence period 

That seems like a short period for a property that has been vacant for 10 years... correct me if I am seeing this the wrong way so that I know how to structure my offers.