diff --git a/public/channels.js b/public/channels.js
index 6e6c8fbe..41f8236b 100644
--- a/public/channels.js
+++ b/public/channels.js
@@ -9,9 +9,14 @@
   let autoScroll = true;
   let nodeCache = {};
   let selectedNode = null;
+  var _nodeCacheTTL = 5 * 60 * 1000; // 5 minutes
 
   async function lookupNode(name) {
-    if (nodeCache[name] !== undefined) return nodeCache[name];
+    var cached = nodeCache[name];
+    if (cached !== undefined) {
+      if (cached && cached.fetchedAt && (Date.now() - cached.fetchedAt < _nodeCacheTTL)) return cached.data;
+      if (cached && !cached.fetchedAt) return cached; // legacy null entries
+    }
     try {
       const data = await api('/nodes/search?q=' + encodeURIComponent(name));
       // Try exact match first, then case-insensitive, then contains
@@ -20,7 +25,7 @@
         || nodes.find(n => n.name && n.name.toLowerCase() === name.toLowerCase())
         || nodes.find(n => n.name && n.name.toLowerCase().includes(name.toLowerCase()))
         || nodes[0] || null;
-      nodeCache[name] = match;
+      nodeCache[name] = { data: match, fetchedAt: Date.now() };
       return match;
     } catch { nodeCache[name] = null; return null; }
   }
diff --git a/public/observers.js b/public/observers.js
index 8c3ce74c..0aa72bc8 100644
--- a/public/observers.js
+++ b/public/observers.js
@@ -11,7 +11,7 @@
       <div class="observers-page">
         <div class="page-header">
           <h2>Observer Status</h2>
-          <button class="btn-icon" data-action="obs-refresh" title="Refresh">🔄</button>
+          <button class="btn-icon" data-action="obs-refresh" title="Refresh" aria-label="Refresh observers">🔄</button>
         </div>
         <div id="obsContent"><div class="text-center text-muted" style="padding:40px">Loading…</div></div>
       </div>`;
@@ -47,11 +47,14 @@
     }
   }
 
+  // NOTE: Comparing server timestamps to Date.now() can skew if client/server
+  // clocks differ. We add ±30s tolerance to thresholds to reduce false positives.
   function healthStatus(lastSeen) {
     if (!lastSeen) return { cls: 'health-red', label: 'Unknown' };
     const ago = Date.now() - new Date(lastSeen).getTime();
-    if (ago < 600000) return { cls: 'health-green', label: 'Online' };    // < 10 min
-    if (ago < 3600000) return { cls: 'health-yellow', label: 'Stale' };   // < 1 hour
+    const tolerance = 30000; // 30s tolerance for clock skew
+    if (ago < 600000 + tolerance) return { cls: 'health-green', label: 'Online' };    // < 10 min + tolerance
+    if (ago < 3600000 + tolerance) return { cls: 'health-yellow', label: 'Stale' };   // < 1 hour + tolerance
     return { cls: 'health-red', label: 'Offline' };
   }
 
@@ -66,9 +69,10 @@
   }
 
   function sparkBar(count, max) {
-    if (max === 0) return '<div class="spark-bar"><div class="spark-fill" style="width:0"></div></div>';
+    const aria = `role="meter" aria-valuenow="${count}" aria-valuemin="0" aria-valuemax="${max}" aria-label="Packet rate"`;
+    if (max === 0) return `<div class="spark-bar" ${aria}><div class="spark-fill" style="width:0"></div></div>`;
     const pct = Math.min(100, Math.round((count / max) * 100));
-    return `<div class="spark-bar"><div class="spark-fill" style="width:${pct}%"></div><span class="spark-label">${count}/hr</span></div>`;
+    return `<div class="spark-bar" ${aria}><div class="spark-fill" style="width:${pct}%"></div><span class="spark-label">${count}/hr</span></div>`;
   }
 
   function render() {
@@ -95,6 +99,7 @@
         <span class="obs-stat">📡 ${observers.length} Total</span>
       </div>
       <table class="data-table obs-table" id="obsTable">
+        <caption class="sr-only">Observer status and statistics</caption>
         <thead><tr>
           <th>Status</th><th>Name</th><th>Region</th><th>Last Seen</th>
           <th>Packets</th><th>Packets/Hour</th><th>Uptime</th>
diff --git a/public/style.css b/public/style.css
index 152670f4..f467f00e 100644
--- a/public/style.css
+++ b/public/style.css
@@ -672,7 +672,8 @@ button.ch-item.selected { background: var(--selected-bg); }
 .health-dot.health-yellow { background: #eab308; box-shadow: 0 0 6px #eab30880; }
 .health-dot.health-red { background: #ef4444; box-shadow: 0 0 6px #ef444480; }
 .obs-table td:first-child { white-space: nowrap; }
-.spark-bar { position: relative; width: 100px; height: 18px; background: var(--border); border-radius: 4px; overflow: hidden; display: inline-block; vertical-align: middle; }
+.spark-bar { position: relative; min-width: 60px; max-width: 100px; flex: 1; height: 18px; background: var(--border); border-radius: 4px; overflow: hidden; display: inline-block; vertical-align: middle; }
+@media (max-width: 640px) { .spark-bar { max-width: 60px; } }
 .spark-fill { height: 100%; background: linear-gradient(90deg, #3b82f6, #60a5fa); border-radius: 4px; transition: width 0.3s; }
 .spark-label { position: absolute; right: 4px; top: 0; line-height: 18px; font-size: 11px; color: var(--text); font-weight: 500; }
 
diff --git a/server.js b/server.js
index 1ca36d11..ffe981bc 100644
--- a/server.js
+++ b/server.js
@@ -1250,7 +1250,7 @@ app.get('/api/observers', (req, res) => {
     const lastHour = db.db.prepare(`SELECT COUNT(*) as count FROM packets WHERE observer_id = ? AND timestamp > ?`).get(o.id, oneHourAgo);
     return { ...o, packetsLastHour: lastHour.count };
   });
-  res.json({ observers: result });
+  res.json({ observers: result, server_time: new Date().toISOString() });
 });
 
 app.get('/api/traces/:hash', (req, res) => {