Sunrise, which almost nobody books
The other end of the day runs the opposite way: earliest sunrise around 05:30 in June, latest around 07:05 in January. Very few people charter for it and the ones who do are usually photographers or fishing parties.
It deserves more attention than it gets, particularly in summer. A 6am departure in July puts you on the flattest water of the year, in genuinely comfortable temperatures, with the entire coast to yourself and the light coming over the city rather than away from it, which is the better direction for photographing the skyline from the sea.
It is also the easiest slot to book. Summer mornings are frequently available the day before, where a weekend sunset in February needs three weeks. For the same money it is the less contested and, in the hot months, the more comfortable half of the day.