When I hear someone say "all day long", I immediately recognize that that individual may be giving a heartfelt impression of his rifle's performance but he doesn't have any real data on which his statement is based. It could mean his rifle performs with a particular best load, or when the shooter is having a good day, or it could be just an idle boast.
In any case, the statement is next to worthless.
Even the best shooting rifles have some ammos and some hand loads that they don't shoot well. I would bet someone could find a load and a bullet type that even the best rifle wouldn't shoot under 1 MOA on average.
In addition, even the best shooters can have an off day or let a couple of rounds mess up a good group. Those groups count when you speak about 'all day long".
So unless the speaker clearly qualifies the conditions and limits that apply to his statement, "all day long" doesn't work for me.