Weekend box office numbers appear within hours of the weekend ending, which is faster than most retail sectors report anything. The speed is possible because the first figures are estimates, and everyone involved treats them as such.
Sunday figures are projections
Studios receive sales data from exhibitors and reporting services through the weekend, then project Sunday's remaining performance from Friday and Saturday patterns.
Those projections are released on Sunday because the news cycle rewards being first, and because the ranking of the weekend is what circulates in coverage.
Monday brings actual receipts, and the revised figures routinely differ from the estimate, occasionally by enough to change the order of the top titles.
The weekend is a defined window
The standard reporting period runs Friday through Sunday, which is a convention rather than a natural unit, since it excludes previews and midweek performance entirely.
Preview screenings held on Thursday evening are usually folded into Friday, which inflates the opening day relative to any later Friday in the run.
Holiday weekends are reported both as three days and as four or five, and the two versions circulate together, which is a frequent source of confusion.
Gross is not what the studio receives
Reported figures are ticket sales at the box office, before the exhibitor takes its share, and that share is set by contract between distributor and cinema.
The split typically favours the distributor most heavily in the first week and shifts towards the exhibitor as a run continues, which shapes release strategy.
Marketing spend does not appear in any of these numbers, so a headline gross says nothing about whether a film has recovered its costs.
Comparisons across time are unstable
Ticket prices rise, so a gross recorded today represents fewer admissions than the same figure recorded years ago, and unadjusted comparisons overstate recent performance.
Premium formats compound this, since a single admission in a large-format auditorium carries a higher price than a standard seat in the same complex.
Admissions counts would be a cleaner measure, and some markets publish them, but the money figure is what gets reported because it is what studios supply.
International reporting follows different rules
Territories report on their own calendars and in their own currencies, and converting them introduces exchange rate effects unrelated to how the film performed.
Release dates are staggered across markets, so a worldwide total is an accumulation of overlapping runs rather than a snapshot of a single weekend.
This is why global figures move in irregular steps, jumping whenever a large market opens rather than tracking any smooth pattern of decline.