diff --git a/daemon/src/oracle.rs b/daemon/src/oracle.rs
index 27479cc..299a567 100644
--- a/daemon/src/oracle.rs
+++ b/daemon/src/oracle.rs
@@ -4,12 +4,12 @@ use crate::model::OracleEventId;
 use anyhow::{Context, Result};
 use async_trait::async_trait;
 use cfd_protocol::secp256k1_zkp::{schnorrsig, SecretKey};
-use futures::stream::FuturesOrdered;
+use futures::stream::FuturesUnordered;
 use futures::TryStreamExt;
 use reqwest::StatusCode;
 use rocket::time::format_description::FormatItem;
 use rocket::time::macros::format_description;
-use rocket::time::{Duration, OffsetDateTime, Time};
+use rocket::time::{OffsetDateTime, Time};
 use serde::Deserialize;
 use std::collections::{HashMap, HashSet};
 use std::ops::Add;
@@ -84,10 +84,14 @@ where
     }
 
     async fn update_latest_announcements(&mut self) -> Result<()> {
-        self.latest_announcements = next_ids()
+        let new_announcements = next_ids()?
             .into_iter()
+            .filter(|event_id| !self.latest_announcements.contains_key(event_id))
             .map(|event_id| async move {
                 let url = event_id.to_olivia_url();
+
+                tracing::debug!("Fetching attestation for {}", event_id);
+
                 let response = reqwest::get(url.clone())
                     .await
                     .with_context(|| format!("Failed to GET {}", url))?;
@@ -102,10 +106,12 @@ where
                     .context("Failed to deserialize as Announcement")?;
                 Result::<_, anyhow::Error>::Ok((event_id, announcement))
             })
-            .collect::<FuturesOrdered<_>>()
-            .try_collect()
+            .collect::<FuturesUnordered<_>>()
+            .try_collect::<HashMap<_, _>>()
             .await?;
 
+        self.latest_announcements.extend(new_announcements); // FIXME: This results in linear memory growth.
+
         Ok(())
     }
 
@@ -200,30 +206,36 @@ impl<CFD: 'static, M: 'static> xtra::Handler<GetAnnouncement> for Actor<CFD, M>
 
 /// Construct the URL of the next 24 `BitMEX/BXBT` hourly events
 /// `olivia` will attest to.
-fn next_ids() -> Vec<OracleEventId> {
-    next_24_hours(OffsetDateTime::now_utc())
+fn next_ids() -> Result<Vec<OracleEventId>> {
+    let ids = next_24_hours(OffsetDateTime::now_utc())?
         .into_iter()
         .map(event_id)
-        .collect()
+        .collect();
+
+    Ok(ids)
 }
 
-fn next_24_hours(datetime: OffsetDateTime) -> Vec<OffsetDateTime> {
-    let adjusted = datetime.replace_time(Time::from_hms(datetime.hour(), 0, 0).expect("in_range"));
-    (1..=24).map(|i| adjusted + Duration::hours(i)).collect()
+fn next_24_hours(datetime: OffsetDateTime) -> Result<Vec<OffsetDateTime>> {
+    let adjusted = ceil_to_next_hour(datetime)?;
+    let timestamps = (0..=24).map(|i| adjusted + i.hours()).collect();
+
+    Ok(timestamps)
 }
 
 #[allow(dead_code)]
 pub fn next_announcement_after(timestamp: OffsetDateTime) -> Result<OracleEventId> {
-    // always ceil to next hour and roll over to next day automatically
+    let adjusted = ceil_to_next_hour(timestamp)?;
 
-    let timestamp = timestamp.add(1.hours());
+    Ok(event_id(adjusted))
+}
 
-    let adjusted = timestamp.replace_time(
-        Time::from_hms(timestamp.hour(), 0, 0)
-            .context("Could not adjust time for next announcement")?,
-    );
+fn ceil_to_next_hour(original: OffsetDateTime) -> Result<OffsetDateTime, anyhow::Error> {
+    let timestamp = original.add(1.hours());
+    let exact_hour = Time::from_hms(timestamp.hour(), 0, 0)
+        .context("Could not adjust time for next announcement")?;
+    let adjusted = timestamp.replace_time(exact_hour);
 
-    Ok(event_id(adjusted))
+    Ok(adjusted)
 }
 
 /// Construct the URL of `olivia`'s `BitMEX/BXBT` event to be attested
@@ -575,7 +587,7 @@ mod tests {
     fn next_24() {
         let datetime = datetime!(2021-09-23 10:43:12);
 
-        let next_24_hours = next_24_hours(datetime.assume_utc());
+        let next_24_hours = next_24_hours(datetime.assume_utc()).unwrap();
         let expected = vec![
             datetime!(2021-09-23 11:00:00).assume_utc(),
             datetime!(2021-09-23 12:00:00).assume_utc(),
@@ -601,6 +613,7 @@ mod tests {
             datetime!(2021-09-24 08:00:00).assume_utc(),
             datetime!(2021-09-24 09:00:00).assume_utc(),
             datetime!(2021-09-24 10:00:00).assume_utc(),
+            datetime!(2021-09-24 11:00:00).assume_utc(),
         ];
 
         assert_eq!(next_24_hours, expected)