Check for New Signatures Before Scheduled Scans Checks for new signatures before running scheduled scans. If you enable this policy setting, the scheduled scan checks for new signatures before it scans the computer. If you disable or do not configure this policy setting, the scheduled scan begins without downloading new signatures.

(1) GPO: Computer Configuration\Administrative Templates\Windows Components\Windows Defender!Check for New Signatures Before Scheduled Scans (2) REG: HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows Defender\Scan!CheckForSignaturesBeforeRunningScan