diff --git a/backend/internal/http/handlers.go b/backend/internal/http/handlers.go
index 54b1079..cd3c21e 100644
--- a/backend/internal/http/handlers.go
+++ b/backend/internal/http/handlers.go
@@ -17,7 +17,9 @@ func NewRouter(svc service.EpisodeService) *gin.Engine {
 		c.JSON(http.StatusOK, gin.H{"status": "ok"})
 	})
 
-	r.GET("/current", func(c *gin.Context) {
+	v1 := r.Group("/v1")
+
+	v1.GET("/current", func(c *gin.Context) {
 		cur, err := svc.GetCurrent(c.Request.Context())
 		if err != nil {
 			if err == repo.ErrNotFound {
@@ -32,10 +34,10 @@ func NewRouter(svc service.EpisodeService) *gin.Engine {
 
 	type setCurrentReq struct {
 		ID        int64  `json:"id" binding:"required"`
-		StartTime string `json:"start_time" binding:"required"` // HH:MM or HH:MM:SS
+		StartTime string `json:"start_time" binding:"required"`
 	}
 
-	r.POST("/current", func(c *gin.Context) {
+	v1.POST("/current", func(c *gin.Context) {
 		var req setCurrentReq
 		if err := c.ShouldBindJSON(&req); err != nil {
 			c.JSON(http.StatusBadRequest, gin.H{"error": "invalid payload"})
diff --git a/backend/internal/service/episode_service.go b/backend/internal/service/episode_service.go
index 5758cae..e046d19 100644
--- a/backend/internal/service/episode_service.go
+++ b/backend/internal/service/episode_service.go
@@ -3,13 +3,13 @@ package service
 import (
 	"context"
 	"errors"
-	"strings"
+	"regexp"
 	"time"
 
 	"watch-party-backend/internal/repo"
 )
 
-var ErrInvalidTime = errors.New("invalid start_time (expected HH:MM or HH:MM:SS)")
+var ErrInvalidTime = errors.New("invalid start_time (expected HH:MM:SS)")
 
 type EpisodeService interface {
 	GetCurrent(ctx context.Context) (repo.Episode, error)
@@ -31,32 +31,27 @@ func (s *episodeService) GetCurrent(ctx context.Context) (repo.Episode, error) {
 }
 
 func (s *episodeService) SetCurrent(ctx context.Context, id int64, start string) (repo.Episode, error) {
-	// normalize and validate time as HH:MM:SS
-	normalized, err := normalizeHHMMSS(start)
-	if err != nil {
+	// Strict HH:MM:SS (24h, zero-padded) — e.g., 20:07:05
+	if !isHHMMSS(start) {
 		return repo.Episode{}, ErrInvalidTime
 	}
 
 	c, cancel := context.WithTimeout(ctx, 5*time.Second)
 	defer cancel()
 
-	// do the transaction
-	if err := s.repo.SetCurrent(c, id, normalized); err != nil {
+	if err := s.repo.SetCurrent(c, id, start); err != nil {
 		return repo.Episode{}, err
 	}
 	// return the new current row
 	return s.repo.GetCurrent(c)
 }
 
-func normalizeHHMMSS(s string) (string, error) {
-	s = strings.TrimSpace(s)
-	if len(s) == 5 { // HH:MM → append seconds
-		s += ":00"
+var hhmmss = regexp.MustCompile(`^(?:[01]\d|2[0-3]):[0-5]\d:[0-5]\d$`)
+
+func isHHMMSS(s string) bool {
+	if !hhmmss.MatchString(s) {
+		return false
 	}
-	// Strict parse/format to 24h
-	t, err := time.Parse("15:04:05", s)
-	if err != nil {
-		return "", err
-	}
-	return t.Format("15:04:05"), nil
+	_, err := time.Parse("15:04:05", s)
+	return err == nil
 }
diff --git a/frontend/src/components/Timer.tsx b/frontend/src/components/Timer.tsx
index 6f43aae..de79772 100644
--- a/frontend/src/components/Timer.tsx
+++ b/frontend/src/components/Timer.tsx
@@ -2,7 +2,7 @@ import { useEffect, useMemo, useRef, useState } from "react";
 
 // ===== Config & fallbacks =====
 const TIMEZONE = "Asia/Tokyo"; // JST (UTC+09)
-const API_URL = "/api/current";
+const API_URL = "/api/v1/current";
 const FALLBACK_START_HOUR = 19;
 const FALLBACK_START_MINUTE = 25;
 const FALLBACK_END_SECONDS = 300;