diff --git a/api/types/maintenance.go b/api/types/maintenance.go
index 9cab6a9ad4765..47a6e55494cd5 100644
--- a/api/types/maintenance.go
+++ b/api/types/maintenance.go
@@ -45,10 +45,10 @@ var validWeekdays = [7]time.Weekday{
 	time.Saturday,
 }
 
-// parseWeekday attempts to interpret a string as a time.Weekday. In the interest of flexibility,
+// ParseWeekday attempts to interpret a string as a time.Weekday. In the interest of flexibility,
 // parsing is case-insensitive and supports the common three-letter shorthand accepted by many
 // common scheduling utilites (e.g. contab, systemd timers).
-func parseWeekday(s string) (day time.Weekday, ok bool) {
+func ParseWeekday(s string) (day time.Weekday, ok bool) {
 	for _, w := range validWeekdays {
 		if strings.EqualFold(w.String(), s) || strings.EqualFold(w.String()[:3], s) {
 			return w, true
@@ -58,6 +58,42 @@ func parseWeekday(s string) (day time.Weekday, ok bool) {
 	return time.Sunday, false
 }
 
+// ParseWeekdays attempts to parse a slice of strings representing week days.
+// The slice must not be empty but can also contain a single value "*", representing the whole week.
+// Day order doesn't matter but the same week day must not be present multiple times.
+// In the interest of flexibility, parsing is case-insensitive and supports the common three-letter shorthand
+// accepted by many common scheduling utilites (e.g. contab, systemd timers).
+func ParseWeekdays(days []string) (map[time.Weekday]struct{}, error) {
+	if len(days) == 0 {
+		return nil, trace.BadParameter("empty weekdays list")
+	}
+	// Special case, we support wildcards.
+	if len(days) == 1 && days[0] == Wildcard {
+		return map[time.Weekday]struct{}{
+			time.Monday:    {},
+			time.Tuesday:   {},
+			time.Wednesday: {},
+			time.Thursday:  {},
+			time.Friday:    {},
+			time.Saturday:  {},
+			time.Sunday:    {},
+		}, nil
+	}
+	weekdays := make(map[time.Weekday]struct{}, 7)
+	for _, day := range days {
+		weekday, ok := ParseWeekday(day)
+		if !ok {
+			return nil, trace.BadParameter("failed to parse weekday: %v", day)
+		}
+		// Check if this is a duplicate
+		if _, ok := weekdays[weekday]; ok {
+			return nil, trace.BadParameter("duplicate weekday: %v", weekday.String())
+		}
+		weekdays[weekday] = struct{}{}
+	}
+	return weekdays, nil
+}
+
 // generator builds a closure that iterates valid maintenance config from the current day onward. Used in
 // schedule export logic and tests.
 func (w *AgentUpgradeWindow) generator(from time.Time) func() (start time.Time, end time.Time) {
@@ -75,7 +111,7 @@ func (w *AgentUpgradeWindow) generator(from time.Time) func() (start time.Time,
 
 	var weekdays []time.Weekday
 	for _, d := range w.Weekdays {
-		if p, ok := parseWeekday(d); ok {
+		if p, ok := ParseWeekday(d); ok {
 			weekdays = append(weekdays, p)
 		}
 	}
@@ -203,7 +239,7 @@ func (m *ClusterMaintenanceConfigV1) CheckAndSetDefaults() error {
 		}
 
 		for _, day := range m.Spec.AgentUpgrades.Weekdays {
-			if _, ok := parseWeekday(day); !ok {
+			if _, ok := ParseWeekday(day); !ok {
 				return trace.BadParameter("invalid weekday in agent upgrade window: %q", day)
 			}
 		}
@@ -248,13 +284,14 @@ func (m *ClusterMaintenanceConfigV1) WithinUpgradeWindow(t time.Time) bool {
 		}
 	}
 
-	weekday := t.Weekday().String()
-	for _, upgradeWeekday := range upgradeWindow.Weekdays {
-		if weekday == upgradeWeekday {
-			if int(upgradeWindow.UTCStartHour) == t.Hour() {
-				return true
-			}
-		}
+	upgradeWeekDays, err := ParseWeekdays(upgradeWindow.Weekdays)
+	if err != nil {
+		return false
 	}
-	return false
+
+	if _, ok := upgradeWeekDays[t.Weekday()]; !ok {
+		return false
+	}
+
+	return int(upgradeWindow.UTCStartHour) == t.Hour()
 }
diff --git a/api/types/maintenance_test.go b/api/types/maintenance_test.go
index 203006a8dee37..464c1a4157637 100644
--- a/api/types/maintenance_test.go
+++ b/api/types/maintenance_test.go
@@ -205,7 +205,7 @@ func TestWeekdayParser(t *testing.T) {
 	}
 
 	for _, tt := range tts {
-		day, ok := parseWeekday(tt.input)
+		day, ok := ParseWeekday(tt.input)
 		if tt.fail {
 			require.False(t, ok)
 			continue
@@ -244,7 +244,7 @@ func TestWithinUpgradeWindow(t *testing.T) {
 			desc: "within upgrade window weekday",
 			upgradeWindow: AgentUpgradeWindow{
 				UTCStartHour: 8,
-				Weekdays:     []string{"Monday"},
+				Weekdays:     []string{"Mon"},
 			},
 			date:         "Mon, 02 Jan 2006 08:04:05 UTC",
 			withinWindow: true,
@@ -253,7 +253,7 @@ func TestWithinUpgradeWindow(t *testing.T) {
 			desc: "not within upgrade window weekday",
 			upgradeWindow: AgentUpgradeWindow{
 				UTCStartHour: 8,
-				Weekdays:     []string{"Tuesday"},
+				Weekdays:     []string{"Tue"},
 			},
 			date:         "Mon, 02 Jan 2006 08:04:05 UTC",
 			withinWindow: false,