DateTime of next 3am occurrence

Question

I'm sure this is very easy, but I've got a sudden mental block.... I'm trying to get a DateTime object for the next occurence of 3am... for example, if DateTime.Now is 16/july/2009 : 12:04pm - the next occurance of 3am would be 17/july/2009 : 03:00

However, if DateTime.Now was 17/july/2009 : 01:00 then the next occurence would still be 17/july/2009 : 03:00 (not the day after) does that make sense?

Answer 1

Dunno a shortcut but you could clone the datetime object you're checking, set the time to 3am and see if its before or after the one you're checking

Answer 2

One option:

DateTime now = DateTime.Now;
DateTime today3am = now.Date.AddHours(3);
DateTime next3am = now <= today3am ? today3am : today3am.AddDays(1);

Another:

DateTime now = DateTime.Now;
DateTime today = now.Date;
DateTime next3am = today.AddHours(3).AddDays(now.Hour >= 3 ? 1 : 0)

Lots of ways of skinning that particular cat :)

This is all in local time of course, which means you don't need to worry about time zones. Life becomes trickier if you want to get time zones involved...

Note that it's a good idea to take DateTime.Now once to avoid problems if the date rolls over while you're calculating...

Answer 3

DateTime now = DateTime.Now;
DateTime threeAM = now.Date.AddHours(3);

if (threeAM < now)
    threeAM = threeAM.AddDays(1);

Answer 4

An alternative (using a function):

DateTime NextAt(TimeSpan time)
{
  DateTime now = DateTime.Now;
  DateTime result = now.Date + time;

  return (now <= result) ? result : result.AddDays(1);
}

call it like:

DateTime next3am = NextAt(new TimeSpan(3,0,0));

Answer 5

You can do it without an if statement (or conditional operator):

// get the current time
DateTime now = DateTime.Now;
// get a 3:00 AM point in time in the future
DateTime next = now.Date.AddHours(24 + 3);
// subtract the number of whole extra days
next = next.AddDays((now - next).Days);

I always explain that you should get the point in time (DateTime.Now) only once in a calculation like this, as it's a changing value, so do I have to repeat it? Well, I just did. ;)

Answer 6

//just add 24 - 3 = 21 hours and get Today (start of day) and Add 3 hour

DateTime now = DateTime.Now.AddHours(21).Today.AddHours(3);