"Not a second more, not a second less."
Translation:Ni un segundo más, ni un segundo menos.
I was going to use Ni un segundo, but checking the hover hint (what had only "no") I used No the "ni and the following negative. These hover hints are counter productive to the learning process. I had to "unlearn" what I thought was correct then "relearn" it again. Maybe this a a basswkards cognitive conditioning.
1) It wouldn't be right in Spanish, because in that case "no un segundo más, no un segundo menos" would literally mean "don't a second more, don't a second less"; which makes no sense.
2) But it would be right in English: That's why we use "no/not" to express an exact amount as in: "ni más ni menos que...", meaning: "no more, no less than..."
In this case, the whole sentence would be: "Me tardé ni más ni menos que (sólo) cinco segundos. Ni un segundo más, ni un segundo menos", mening: "It took me no more, no less than (just) five seconds. Not a second more, not a second less."
Because the speaker is traying to say it took them an exact amount of time to do something: It didn't took them ×+1 or x-1 seconds. No, it took them exactly × seconds.
Please, read my other replies on this thread to catch the whole meaning behind the idea of "ni un segundo más, ni un segundo menos".