So thinking about my Novel's opening I have the sentence, "That was the third one tonight." It is narration, not dialogue. In past tense telling one would say, "It was the third one that night." I could change it to internal dialogue and make it a thought which would fix the tense problem. I think I'm over thinking my character's first person narration. It's not like the narrator is telling people a story, rather she's the POV the story is narrated through, but it's past tense, not present tense. Aaaarrrrgghhh!
Well, my skillset isn't overly attuned to tense issues but here's my take: That was the third one toinight - sounds a lot like a narrator playing story teller as if it was the present. Kinda like a voice over we see in movies. Nothing wrong with but I don't think you can switch in and out of it willy-nilly. The latter sounds more like the standard past tense narrative that we're used to reading in modern literature.
The example in your first line would make sense if the night is still happening and the event happened earlier that night. It's like saying, "We witnessed a car crash today." This implies that the car crash occurred earlier that same day.
Already happened, tonight. Already happened, possibly tonight, possibly some other night. Context clues needed. ---------------------- So, it depends in which one is meant.
Seems too much like a fad to me and I'm not sure I like it. Some people can carry it off well, I'm not saying they shouldn't. But it's not for me at the moment.
I asked a similar question here: https://www.writingforums.org/threads/past-and-present-tense.132407/ The comments may shed more light on the issue. I'm still not sure which way to go. Every option seems to be problematic in some way.
Or come up with a new opening sentence? If it has to be either of those, however, I'd use "it was the third one that night" if you're writing in 3rd person + past tense. It may sound a bit like an omni narrator, but what I've read on the subject, it's actually ok to sometimes take a little distance to the POV you're filtering the story through. A beginning of the novel or a chapter can be a good place to employ that technique.
Just get rid of the "tonight" and use description to show the reader it's nighttime? It already happened three times. It happened for the third time already. It happened three times--so far. I have no context to go off of, so bare with me: I sat in my room, moonlight showing the beads of sweat on my skin. It happened three times--so far.
That's not what I'm attached to. I'm attached to the character's voice in the scene and don't want to change it for grammar pedantry. I did, however, want to learn more about writing past tense properly regardless.