Perfecto vs Indefinido with specific times

Question

Finding this lesson on Kwiziq has proved a real revelation for me! I've been learning Spanish for the last 3-4 years through online courses geared toward Latin American Spanish and wasn't aware of this difference. I've always been aware of some regional vocabulary differences but, since I've geared my learning toward Peninsular Spanish (which I need), I'm now finding quite a few grammatical differences too. I had seen the perfect used in this way in El País articles and books etc but I'd not been able to find any resource that actually explained it... until now!

Could you answer how specific times might influence choose of tense?

I spoke to him at 3am this morning

His flight left at 6pm today

These specific times seem to indicate start and finish times. Do they point toward preterite?

Answer

Hola Graeme,
First of all, we are glad to hear you find that lesson very useful. This seems to be one of the things that take quite a long time to "master" because of the different use of tenses in English and because of the different use of tenses in Spain and Latin America, so, a student used to Latin American Spanish usually finds the use of the perfect tense a bit confusing in certain contexts as the past simple is preferred in Latin America in those same contexts. 
With reference to your two sentences:
1. I spoke to him at 3am this morning 
The fact that we are seeing a precise time  makes us think straight away about the Indefinido (past simple) , as a completed action, specific time in the past, so we could say:
1a. Hablé con él a las 3 de la mañana.
However, if we used the time phrase "esta mañana"  we could also use the perfect tense, even thought the sentence is still stating a specific time:
1b. He hablado con él esta mañana a las 3. 
But, because we have both time phrases in the sentence I would say both are accepted. It will depend on the speaker, focusing more in the fact that it was at 3 am, or focusing more in the fact that it was this morning -this generally been considered a time phrase still connected to the present time in a native mind.
 
2a. Su vuelo salió a las 6 de la tarde. 
Again, the same case as the other sentence. Here we are focusing more on the time when it happened, as a specific time - past simple. 
However:
2b. Su vuelo ha salido hoy a las 6 de la tarde.
Hoy is a time phrase where the speaker still considers him/herself inside of, connected to the present, so, using hoy will trigger the perfect tense, despite having again a specific time. 
Here, I personally think the use of the past simple would not be common in Spain. It is to do with the word "hoy". Even thought you have the precise time "hoy a las 6" using the past simple would sound a bit odd. 
As you can see, there is no magic formula to always know which one to use. There is a general rule, but also little nuances to take into account. 
I hope this helped.
Un saludo,
Inma