diff --git a/playbook/shopfloor-setup/common/scripts/Backup-PartMarker.ps1 b/playbook/shopfloor-setup/common/scripts/Backup-PartMarker.ps1
index 824343f..9f4c217 100644
--- a/playbook/shopfloor-setup/common/scripts/Backup-PartMarker.ps1
+++ b/playbook/shopfloor-setup/common/scripts/Backup-PartMarker.ps1
@@ -46,6 +46,12 @@
 # Always exits 0 so the GE-Enforce "last run result" stays clean. Failures are
 # logged, never thrown.
 
+# CmdletBinding so an unknown argument is an ERROR, not a shrug. Without it a
+# script's param block silently drops unrecognised named arguments into $args -
+# so a typo in the manifest entry's Args ("-WindowStartMinutes 45") would be
+# ignored and the capture would quietly run at the wrong time, with nothing in
+# the log to say why. Cost me an hour of debugging a gate that was fine.
+[CmdletBinding()]
 param(
     [string]$BaseUrl = '',
     # Root of the opaque-backup tree. The snapshot lands in
@@ -80,6 +86,12 @@ param(
     # GE-Enforce fires every 5 minutes, so this runs on the first cycle inside
     # the hour and the 24h throttle stops it running again that day.
     [int[]]$WindowHours = @(14),
+    # Minute the window OPENS within those hours. 0 means the whole hour.
+    # Set from the manifest entry's Args when the first run of the day should
+    # land at a particular time - the shift change is a moment, not an hour,
+    # and a capture is easiest to watch when somebody expects it.
+    [ValidateRange(0, 59)]
+    [int]$WindowStartMinute = 0,
     # Used ONLY once the backup is overdue - the other two shift changes. They
     # are unattended, so they are a fallback for a bay that is busy at 14:00
     # every day, not part of the normal schedule.
@@ -178,7 +190,11 @@ if ($MyInvocation.InvocationName -eq '.') { return }
 # out-of-window cycle costs a clock read and nothing else.
 if (-not $Force) {
     $now = Get-Date
-    $inwindow = ($WindowHours -contains $now.Hour)
+    # Both the hour AND the minute, so a window can be "14:45 onwards" rather
+    # than the whole of the 14:00 hour. GE-Enforce fires every 5 minutes, so
+    # the capture starts on the first cycle at or after that time and the 24h
+    # throttle stops it running again that day.
+    $inwindow = ($WindowHours -contains $now.Hour) -and ($now.Minute -ge $WindowStartMinute)
 
     # The marker file is stamped on every post attempt, so its age answers
     # "when did a capture last get through" - which is what the escalation
@@ -213,7 +229,8 @@ if (-not $Force) {
     # marking parts and the port is not ours to take.
     $allowed = $inwindow
     if (-not $allowed -and $overdue) {
-        $allowed = ($OverdueWindowHours -contains $now.Hour)
+        $allowed = ($OverdueWindowHours -contains $now.Hour) -and
+                   ($now.Minute -ge $WindowStartMinute)
     }
 
     if (-not $allowed) {
@@ -232,7 +249,7 @@ if (-not $Force) {
             # was built to stop.
             Write-ShopdbQuietState -Kind $KIND -State 'outside-window' -Message (
                 'Outside the capture window ({0}). The marker port is shared with eDNC, so the daily capture waits for a shift change. Use -Force to override.' -f
-                (($WindowHours | ForEach-Object { '{0:00}:00' -f $_ }) -join ', '))
+                (($WindowHours | ForEach-Object { '{0:00}:{1:00}' -f $_, $WindowStartMinute }) -join ', '))
         }
         exit 0
     }