How long does it take the underwritter to approve a loan applica

How long does it take the underwritter to approve a loan application?

The loan processor just gave me an update saying the following:

>>>> I reviewed the assets and sent your file to the underwriter last night to review as well.

>>>> It looks ok to me, but he is the final. 

Usually how long does it take the underwritter to approve a mortgage application? Do I need to worry about it? Or do I need to look some other quick alternatives such as line of credits?

Thanks.