diff --git a/server/routes.ts b/server/routes.ts
index dd27996..f288d0b 100644
--- a/server/routes.ts
+++ b/server/routes.ts
@@ -294,26 +294,33 @@ export async function registerRoutes(app: Express): Promise<Server> {
     }
   });
 
-  // Get guards availability for general planning
+  // Get guards availability for general planning with time slot conflict detection
   app.get("/api/guards/availability", isAuthenticated, async (req, res) => {
     try {
-      const { weekStart, siteId, location } = req.query;
+      const { start, end, siteId, location } = req.query;
       
-      if (!weekStart || !siteId || !location) {
+      if (!start || !end || !siteId || !location) {
         return res.status(400).json({ 
-          message: "Missing required parameters: weekStart, siteId, location" 
+          message: "Missing required parameters: start, end, siteId, location" 
         });
       }
       
-      const weekStartDate = parseISO(weekStart as string);
-      if (!isValid(weekStartDate)) {
-        return res.status(400).json({ message: "Invalid weekStart date format" });
+      const startDate = parseISO(start as string);
+      const endDate = parseISO(end as string);
+      
+      if (!isValid(startDate) || !isValid(endDate)) {
+        return res.status(400).json({ message: "Invalid date format for start or end" });
+      }
+      
+      if (endDate <= startDate) {
+        return res.status(400).json({ message: "End time must be after start time" });
       }
       
       const availability = await storage.getGuardsAvailability(
-        weekStartDate,
         siteId as string,
-        location as string
+        location as string,
+        startDate,
+        endDate
       );
       
       res.json(availability);
@@ -1681,6 +1688,48 @@ export async function registerRoutes(app: Express): Promise<Server> {
     }
   });
 
+  // Create shift assignment with planned time slots
+  app.post("/api/shifts/:shiftId/assignments", isAuthenticated, async (req, res) => {
+    try {
+      const { shiftId } = req.params;
+      const { guardId, plannedStartTime, plannedEndTime } = req.body;
+      
+      if (!guardId || !plannedStartTime || !plannedEndTime) {
+        return res.status(400).json({ 
+          message: "Missing required fields: guardId, plannedStartTime, plannedEndTime" 
+        });
+      }
+      
+      // Validate times
+      const startDate = new Date(plannedStartTime);
+      const endDate = new Date(plannedEndTime);
+      
+      if (isNaN(startDate.getTime()) || isNaN(endDate.getTime())) {
+        return res.status(400).json({ message: "Invalid date format for plannedStartTime or plannedEndTime" });
+      }
+      
+      if (endDate <= startDate) {
+        return res.status(400).json({ message: "plannedEndTime must be after plannedStartTime" });
+      }
+      
+      // Create assignment
+      const assignment = await storage.createShiftAssignment({
+        shiftId,
+        guardId,
+        plannedStartTime: startDate,
+        plannedEndTime: endDate,
+      });
+      
+      res.json(assignment);
+    } catch (error: any) {
+      console.error("Error creating shift assignment with time slot:", error);
+      if (error.message?.includes('overlap') || error.message?.includes('conflict')) {
+        return res.status(409).json({ message: error.message });
+      }
+      res.status(500).json({ message: "Failed to create shift assignment" });
+    }
+  });
+
   // ============= NOTIFICATION ROUTES =============
   app.get("/api/notifications", isAuthenticated, async (req: any, res) => {
     try {