GA4 processes most standard reports within 24 hours, but the Realtime report shows activity with only a few seconds of latency—usually under 10 seconds for active sessions. If you're watching traffic from a campaign you just launched, you'll see clicks and conversions appear almost immediately in the Realtime view. Standard reports like Acquisition, Engagement, and Monetization typically reflect complete data within 4–8 hours, though Google states up to 24 hours for full processing. Complex calculations (like attribution models or audience building) can take 24–48 hours to finalize, especially if you're working with large data volumes or have sampling applied. The delay exists because GA4 runs data through processing pipelines—deduplication, bot filtering, cross-device stitching, and event parameter validation all happen before numbers lock in. You might notice slight fluctuations in yesterday's data if you check reports multiple times in a day; that's normal as late-arriving hits get processed. For clients at Ottawa SEO, we never make optimization decisions based on same-day data unless we're monitoring a live issue. We pull reports at least 48 hours after the date range ends to avoid incomplete datasets. If you're running paid campaigns and need faster feedback, set up real-time custom reports or use Google Ads' native interface, which updates every few minutes. One gotcha: data thresholds in GA4 can temporarily hide rows in reports when user counts are low, even if the data has processed. You'll see a warning icon when this happens. Also, if you modify events or conversions in your GA4 setup, those changes only apply going forward—historical data doesn't reprocess. The latency is a tradeoff for accuracy and privacy compliance, and it's why we always compare week-over-week or month-over-month rather than obsessing over hourly changes.