You mentioned that we are not using whole fights but how about short ones? Like, 2-3 swings short?
Yeah, short fights would be fine to count as one moment. Ones that would be equal to maybe a few pages in a manga or even ones that are most of one chapter and can't be broken down well into multiple moments could be fine. With that rule it was more designed to stop people from nominating things like "Luffy's fight against Lucci" as one moment when it was far too long to be just one I think.
There are other instances where breaking down what counts as a "moment" might be tough and I'll wait until the nominations are in to narrow down the moments more if need be. I was having a talk with beakedbard about the "Strawhats declare war on the WG" moment and if that also includes Robin's "I want to live" moment. The two happen so close together (the anime clip of both happening together is just a few mins) that I think counting them as the same moment would be okay. So we might encounter more things like that.