diff --git a/src/rules/validators/end-time.ts b/src/rules/validators/end-time.ts
index 5514ba9..7e88881 100644
--- a/src/rules/validators/end-time.ts
+++ b/src/rules/validators/end-time.ts
@@ -8,10 +8,10 @@ export const validateEndTime: RuleValidator = (rule) => {
 	}
 
 	if (typeof rule.endTime !== "string") {
-		throw new Error("endTime must be a string in HH:mm format");
+		throw new Error("endTime must be a string in HH:mm or HH:mm:ss format");
 	}
 
-	if (!isMatch(rule.endTime, "HH:mm")) {
-		throw new Error(`endTime must be in HH:mm format (e.g., "09:30", "23:45"), got: "${rule.endTime}"`);
+	if (!isMatch(rule.endTime, "HH:mm") && !isMatch(rule.endTime, "HH:mm:ss")) {
+		throw new Error(`endTime must be in HH:mm or HH:mm:ss format (e.g., "09:30", "23:45:00"), got: "${rule.endTime}"`);
 	}
 };
diff --git a/src/rules/validators/start-time.ts b/src/rules/validators/start-time.ts
index bf9d9fb..0da7434 100644
--- a/src/rules/validators/start-time.ts
+++ b/src/rules/validators/start-time.ts
@@ -8,10 +8,12 @@ export const validateStartTime: RuleValidator = (rule) => {
 	}
 
 	if (typeof rule.startTime !== "string") {
-		throw new Error("startTime must be a string in HH:mm format");
+		throw new Error("startTime must be a string in HH:mm or HH:mm:ss format");
 	}
 
-	if (!isMatch(rule.startTime, "HH:mm")) {
-		throw new Error(`startTime must be in HH:mm format (e.g., "09:30", "23:45"), got: "${rule.startTime}"`);
+	if (!isMatch(rule.startTime, "HH:mm") && !isMatch(rule.startTime, "HH:mm:ss")) {
+		throw new Error(
+			`startTime must be in HH:mm or HH:mm:ss format (e.g., "09:30", "23:45:00"), got: "${rule.startTime}"`,
+		);
 	}
 };
diff --git a/test/utils.spec.ts b/test/utils.spec.ts
index 0c78e43..49bb234 100644
--- a/test/utils.spec.ts
+++ b/test/utils.spec.ts
@@ -132,4 +132,11 @@ describe("timeStringToMinutes", () => {
 	it("should handle end of day", () => {
 		expect(timeStringToMinutes("23:59")).to.equal(1439);
 	});
+
+	it("should accept HH:mm:ss but ignore seconds in calculation", () => {
+		expect(timeStringToMinutes("00:00:30")).to.equal(0);
+		expect(timeStringToMinutes("12:30:30")).to.equal(750);
+		expect(timeStringToMinutes("09:30:00")).to.equal(570);
+		expect(timeStringToMinutes("23:59:59")).to.equal(1439);
+	});
 });