This is expected behavior. Spend metrics are finalized after approximately 3 days.
Please see https://dev.twitter.com/ads/analytics.
billed_charge_local_micro provides a real-time view into the estimated cost of a campaign. After three days, the official billed result will be available with the billed_charge_local_micro and billed_engagements metrics.
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.
Please note that spend metrics are not available for dates before 2013-10-10.
