Is there a way to turn off or extend the time on the navigation scroll?

You will have to manually edit the code to achieve that, however it’s not so hard.

Locate
jquery.custom.js under you theme files and on line 130 and 132, you can modify the timing between scroll by replacing 500 in the code:

$("html:not(:animated),body:not(:animated)").animate({ scrollTop: destination - $("#header").outerHeight() }, 500 );

Just replace the ’500′ with the gap you want. 100 is equal to 1 second.