If you go to Analytics
You can read:
As soon as stats are available, you are able to retrieve them. The feedback on stats is real-time. These early results are estimates, the stats are finalized after 24 hours, except for spend metrics. Keep in mind that the API rate limit window is 1 minute long, and too-frequent requests against the stats API endpoints will trigger the rate limit. Partners should detect rate limiting and wait for rate limit windows to reset before retrying queries that were throttled.
Billed versus Estimates
The BILLINGmetrics group provides a real-time view into the estimated cost of a campaign. After three days, the official billed result will be available through the BILLING metric group’s billed_charge_local_micro and billed_engagements.
All billing stats are generally final within 3 days of the event (~99%), however we do process some spam filtering for up to 14 days from the date of the event.
So, what you’re getting its quite normal