When you enable once-daily audits (AMP Setup > General page :: General section :: Device Configuration Audit Interval: Daily) we set the audit time to the time that nightly maintenance starts. After that, re-setting the time for nightly maintenance doesn't affect the daily audit timing.
In 6.4, the time for the next scheduled audit is stored on a per-device basis and is updated when a manual audit is done. So if your devices are set for 4am audits, then you manually audit an AP at 11am, the daily audits for that AP will happen at 11am after that.
In 7.0, the daily audit will take place at the beginning of nightly maintenance.
(In 6.3 and all prior versions, daily audits happened every time the daemons were started, which usually happened to be right after nightly maintenance.)