Why is SKAdNetwork data delayed? What are the looping timers?

SKAN involves two different timers:

• Conversion window timer. This timer starts at 24 hours when the app is launched for the first time. It resets back to 24 hours each time the conversion value is successfully updated. Once this timer expires, all data in the postback is final and cannot be updated.
• Randomization delay. This begins when the conversion window timer expires. Its length is up to 24 hours, arbitrarily chosen by iOS. At the end of this delay, the device sends the postback.

(Note: these terms are not official from Apple's documentation, but we find them useful to avoid confusion)

This means the earliest an ad network can possibly receive the SKAN postback is slightly over 24 hours after install, and that assumes no conversion-value updates are made. Many large networks are currently recommending that conversion value updates be limited to the first 24 hours after install.