Timespan between Now and Next Hour?

This seems to be the most simple:

3600 - DateTime.Now.TimeOfDay.TotalSeconds % 3600

(if you want it in whole numbers - integer - then prefix DateTime.Now... with (int).

Just round the time of day in hours up to the next integral value:

var timeOfDay = DateTime.Now.TimeOfDay;
var nextFullHour = TimeSpan.FromHours(Math.Ceiling(timeOfDay.TotalHours));
var delta = (nextFullHour - timeOfDay).TotalSeconds;

//Completely misread. Completely re-writing

I woudl just do something Like this

int minutesToNextHour = 60 - DateTime.Now.Minutes;
int secondsToNextHour = minutesToNextHour * 60;