Jisho.org Forum

I think you can only use ございました if you're sightly late in an activity that you usually do at the mornings
i.e: if you wake up early and by some reason you oversleep, you should greet everyone by saying おはようございました
...and about your incident, [IMO] you use this only if you're talking to family or job since they want to know the motive of the delay afterwards or even expect an explanation of you. Besides this, it's just the same as saying "Good night" at noon to someone at the street.[/IMO]
btw, it's MOST common you just say the correct phase in the correct time, so ohayou = good morning , konnichiwa = hello (or good afternoon) and konbanwa = good night...
oh, and just you know, ました is the ending of any -ます verb in the past... it's pretty obvious but it helps you quite a lot.
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I have a question relating to this.
I was watching a live broadcast from a japanese convention (vanafest 2010) last night and they would always say ありがとうございました when thanking someone/everyone. would it be because of the fact it was a live broadcast and they were ahead of the western viewers?

As niokun said, ございました is just the past tense of ございます。 So ありがとうございました is just thanking somebody for something that they have already done. (When I first when to Japan--before I studied Japanese--I asked an older Japanese guy on a train about this, and he say people just say ありがとうございます not ありがとうございました (which is clearly false). 30 seconds later, the woman says over the speaker on the train (something something something) ありがとうございました. I pointed this out to him and he seemed confused.)

As for おはようございました, this is not a normal usage. If you don't make it in time for おはようございます (usually till 11am or noon, but depends on the person) you would normally use こんにちは. It's probably either a joke, or a local dialect (apparently they say this in Hokkaido in the late morning).

Here is a good explanation for the difference between "ありがとうございます" and "ありがとうございました".

http://home.alc.co.jp/db/owa/jpn_npa?stage=2&sn=189

Basically, ありがとうございました is used for what was done in the past, for example, 先日はわざわざお越しいただきましてありがとうございました. However, if you want to express that your gratefulness toward the person for what he/she was done in the past does not change even now, you could still say ありがとうございます(present tense), like 先日はわざわざお越しいただきましてありがとうございます.

It's common to say おはよう if it's the first time you see someone during the day regardless of the time. I go into work at 1pm and all my co-workers always say おはよう. For ありがとう it's a little easier, you use future for continuing actions or actions which are repeated in the future and past for completed. But like with おはよう, past and future can be switched around sometimes and the meaning is the same. My instinct says don't worry about it, but if you want more direction, I'd use past when it's more of an interjection than a greeting. i.e. Something said that is said to end of a conversation or prevent starting one.