The better question is how long is your layover, and what would you like to do in Amsterdam?

All I can really tell you is that the train from AMS to Centraal is about 15-20 minutes. Other than the Red Light District and canal tours, most tourist spots are a long walk, tram ride, or taxi away from Centraal. Of course you'll have to go through the usual checkpoints before leaving AMS (which have never taken me very long), and you'll want to get back at least 90 mins before your onward flight.

The rest of your budgeted time depends on what you want to do in Amsterdam.

I'm not familiar with DL so won't try to answer that with my *Alliance knowledge.