Dawn, sunrise, sunset and dusk are the best time of the day for outdoor photography. No secret there. But light changes fast and doesn't last, so for travel photography, be aware and be ready.
Here's sunset and the Statue of Liberty.
Sidenote, in this particular situation, where the subject is three kilometres away (so you need all the "zoom" you can get and then some), cold temperature is your friend as there is less humidity, fog or pollution between you and what you shoot. It was freezing cold...
And after sunset (30-60 minutes) wait for magic hour, when artificial light matches natural light.
(A better example of magic hour is the previous post's picture of Manhattan view from 30 Rock)