diff --git a/RssCloud/Subscriber.php b/RssCloud/Subscriber.php
index 3475237..9159cc4 100644
--- a/RssCloud/Subscriber.php
+++ b/RssCloud/Subscriber.php
@@ -27,7 +27,8 @@ public function __construct(
 	 * or when the lease is old enough that the cloud server has probably expired it.
 	 *
 	 * rssCloud has no lease negotiation — the server does not tell us how long the subscription
-	 * lasts — so this is purely a local timer. The conventional expiry is around 24 hours.
+	 * lasts — so this is purely a local timer. Subscriptions expire after 25 hours and are meant to
+	 * be renewed every 24 (http://walkthrough.rsscloud.co/).
 	 *
 	 * @param RssCloudState $state
 	 */
diff --git a/configure.phtml b/configure.phtml
index da4ada7..204278a 100644
--- a/configure.phtml
+++ b/configure.phtml
@@ -48,7 +48,7 @@
 	<div class="form-group">
 		<label class="group-name" for="renew_hours"><?= _t('ext.rsscloud.renew_hours') ?></label>
 		<div class="group-controls">
-			<input type="number" name="renew_hours" id="renew_hours" min="1" max="168"
+			<input type="number" name="renew_hours" id="renew_hours" min="1" max="<?= RssCloudExtension::MAX_RENEW_HOURS ?>"
 				value="<?= (int)($this->renewSeconds() / 3600) ?>" />
 			<p class="help"><?= _i('help') ?> <?= _t('ext.rsscloud.renew_hours.help') ?></p>
 		</div>
diff --git a/extension.php b/extension.php
index 612307f..9fced78 100644
--- a/extension.php
+++ b/extension.php
@@ -25,12 +25,22 @@ final class RssCloudExtension extends Minz_Extension {
 	public const NAME = 'rssCloud';
 
 	/**
-	 * rssCloud has no lease negotiation, and the protocol documentation does not state an expiry.
-	 * The convention among implementations is around 24 hours, so renew slightly early — the same
-	 * policy core applies to WebSub leases in `FreshRSS_Feed::pubSubHubbubPrepare()`.
+	 * rssCloud has no lease negotiation: the `pleaseNotify` response carries no duration. The rule
+	 * is documented instead — subscriptions expire after 25 hours and must be renewed every 24
+	 * (http://walkthrough.rsscloud.co/). Renewing at 23 stays an hour inside that requirement and
+	 * leaves two hours before expiry, which is the margin {@see self::MAX_SUBSCRIPTIONS_PER_RUN}
+	 * eats into when many subscriptions fall due at once. Core applies the same renew-early policy
+	 * to WebSub leases in `FreshRSS_Feed::pubSubHubbubPrepare()`.
 	 */
 	public const DEFAULT_RENEW_HOURS = 23;
 
+	/**
+	 * Renewing later than the documented 24-hour rule cannot work: the subscription is already gone
+	 * by 25 hours, so every larger value simply lets it lapse. Clamped on the read path rather than
+	 * only in the form, so a hand-edited configuration cannot get past it either.
+	 */
+	public const MAX_RENEW_HOURS = 24;
+
 	/** How stale a cloud-covered resource may get before we poll it anyway, as a safety net. */
 	public const DEFAULT_MAX_STALENESS_HOURS = 24;
 
@@ -135,7 +145,8 @@ public function isPollingSkipped(): bool {
 	}
 
 	public function renewSeconds(): int {
-		return max(1, $this->getSystemConfigurationInt('renew_hours') ?? self::DEFAULT_RENEW_HOURS) * 3600;
+		$hours = $this->getSystemConfigurationInt('renew_hours') ?? self::DEFAULT_RENEW_HOURS;
+		return min(self::MAX_RENEW_HOURS, max(1, $hours)) * 3600;
 	}
 
 	public function maxStalenessSeconds(): int {
diff --git a/i18n/en/ext.php b/i18n/en/ext.php
index cfcdd72..01ca433 100644
--- a/i18n/en/ext.php
+++ b/i18n/en/ext.php
@@ -17,7 +17,7 @@
 		'regenerate_token' => 'Regenerate callback token',
 		'regenerate_token.help' => 'Changes the secret path segment of the callback. Existing subscriptions stop being delivered until they are renewed.',
 		'renew_hours' => 'Renew subscriptions after (hours)',
-		'renew_hours.help' => 'rssCloud does not negotiate a lease duration. Most servers expire subscriptions after about 24 hours, so renew slightly sooner than that.',
+		'renew_hours.help' => 'rssCloud does not negotiate a lease duration. Subscriptions expire after 25 hours and are meant to be renewed every 24, so the default of 23 leaves a margin. Anything above 24 would simply lapse, and is capped.',
 		'skip_polling' => 'Skip polling covered resources',
 		'skip_polling.help' => 'Stop polling a resource on a timer while its cloud subscription is healthy. It is still polled if it goes stale, or when refreshed individually.',
 	),