All creative types use
[delayed impressions](https://support.google.com/admanager/answer/2521337).
This means that impressions aren't counted until the creative renders and
sends an impression request back to Google. Because of this secondary request,
[RTB breakout](https://support.google.com/authorizedbuyers/answer/6156706) and
[RTB Troubleshooting](https://developers.google.com/authorized-buyers/apis/guides/v2/rtb-troubleshooting)
can return a greater number of winning bids than billable impressions.

## Expiration windows

The expiration window for impressions-based billing events varies by inventory
type. The expiration window of the request in seconds is sent in the
`BidRequest.imp.exp` field.

> [!IMPORTANT]
> **Important:** Google records and bills for all impressions received within the following time periods. \* [App Open](https://support.google.com/admanager/answer/9351867) requests: 4 hours \* [Server-side](https://support.google.com/admanager/answer/6147120) requests: 4-6 hours \* [Podded in-stream](https://support.google.com/admanager/answer/2554762) video inventory: 4-6 hours \* All other inventory: 1 hour