Greetings and time of day
dias, tardes, noches....
What time to use which one?
Tardes between 13:00 and 19:00?
Does it depend on what country you're in?
¡Gracias!
4 Answers
Although there may be some regional differences, generally speaking it's like this:
Buenos días until noon.
Buenas tardes until dark.
Buenas noches at dusk till midnight.
After that, it's technically buenos días again, but I'm usually asleep then so I don't know what people say at that time. 
Buenos dias: good day or good morning
buenos tardes: good afternoon
Buenos noches good night
Dias = day or morning
tardes= afternoon
noches = night
you would use Buenas tardes 12:01 to 18:00
Hello rprager,
Welcome to the SpanishDict forum
You asked:
Greetings and time of day dias, tardes, noches....What time to use which one? Tardes between 13:00 and 19:00? Does it depend on what country you're in? ¡Gracias!
Yes, there are/can be some minor variations on account of regional differences. Daniela has given you a very good answer which gives you the general overview. I have chosen to provide an answer that relates specifically to Spain based on what my native teacher told me some time ago and my personal observations. I hope this information will prove helpful. (It may be that Txusta boy or another native Spanish-speaker or Annierats or someone else living there may choose to disagree ...that's fine by me, I am not claiming to be a world authority on this subject.)
I remember asking my native Spanish teacher about this one day in a Skype class. She lives in Murcia, Spain (but comes from Toledo, near Madrid) and she told me that in Spain they normally use:
Buenos días = (which means) Good morning, from around the time you get up in the morning eg: 7am in the morning until between 12 and 2 pm in the afternoon when they have lunch...then they use:
Buenas tardes = Good afternoon/Good evening from about 2pm onwards until supper time/ after they have had dinner (supper) which can often be from 8 or 9 pm onwards.
From what I have also observed while staying on holiday in both northern and southern Spain, that the Spanish people in Spain often eat their evening meal much later than we do in England (this is not a criticism!)...and in the summer months while on holiday, because many of them take a siesta (afternoon rest), children as young as 7 and soemtimes 5 can be observed staying up late with their parents at restaurants, having a meal at 9 or ten at night. Each family is different so there will obviously be differences! 
They usually say (use) Buenas noches = (which means) Good night when they go to bed or for example, when friends leave a social event such as restaurant or party and go back to their separate homes!
Finally, of course you could simply avoid any social embarrassment if you happen to forget by simply saying 'hola'. I have even heard some Spanish natives using: "buenas" which I believe is a colloquial way to say Hello. I am not sure how common/widespread is the use of this word.
I hope this helps
I am open to correction in all respects, as usual, so please feel free to correct me on matters relating to social behavour, in a respectful way!
I am sure it varies depending on the area.
Here: "buenos días" is in the morning until around noon then there is a transition period where you will hear both. Around 1:00 you will mostly hear " buenas tardes" with an occasional "buenos días".
Close to dark if meeting "buenas tardes" if departing "buenas noches" can be used also.
After dark "buenas noches" except after midnight if you are departing "buenas noches" but if meeting "buenos días" is used also.
If someone wakes up regardless of the hour you can use "buenos días" in the same way you would say good morning.
Also when walking and pass by someone you are not going to stop and talk to the norm is "audios" but it is not a problem to say something else or nothing at all if they are silent.
But the best part about being here is when in doubt just say "pura vida".
