diff --git a/src/moonfire-db-test.cc b/src/moonfire-db-test.cc
index b3bd1bf..d2245f0 100644
--- a/src/moonfire-db-test.cc
+++ b/src/moonfire-db-test.cc
@@ -291,6 +291,31 @@ TEST(AdjustDaysMapTest, Basic) {
   EXPECT_THAT(days, testing::ElementsAre());
 }
 
+TEST(GetDayBoundsTest, Basic) {
+  int64_t start_90k;
+  int64_t end_90k;
+  std::string error_msg;
+
+  // Normal day.
+  EXPECT_TRUE(GetDayBounds("2015-12-31", &start_90k, &end_90k, &error_msg))
+      << error_msg;
+  EXPECT_EQ(INT64_C(130639392000000), start_90k);
+  EXPECT_EQ(INT64_C(130647168000000), end_90k);
+
+  // Spring forward (23-hour day).
+  EXPECT_TRUE(GetDayBounds("2016-03-13", &start_90k, &end_90k, &error_msg));
+  EXPECT_EQ(INT64_C(131207040000000), start_90k);
+  EXPECT_EQ(INT64_C(131214492000000), end_90k);
+
+  // Fall back (25-hour day).
+  EXPECT_TRUE(GetDayBounds("2016-11-06", &start_90k, &end_90k, &error_msg));
+  EXPECT_EQ(INT64_C(133057404000000), start_90k);
+  EXPECT_EQ(INT64_C(133065504000000), end_90k);
+
+  // Unparseable day.
+  EXPECT_FALSE(GetDayBounds("xxxx-xx-xx", &start_90k, &end_90k, &error_msg));
+}
+
 // Basic test of running some queries on an empty database.
 TEST_F(MoonfireDbTest, EmptyDatabase) {
   std::string error_message;
diff --git a/src/moonfire-db.cc b/src/moonfire-db.cc
index 96da195..d2fe1d8 100644
--- a/src/moonfire-db.cc
+++ b/src/moonfire-db.cc
@@ -47,6 +47,9 @@ namespace moonfire_nvr {
 
 namespace {
 
+const char kDayFmt[] = "%Y-%m-%d";
+constexpr size_t kDayFmtBufSize = sizeof("YYYY-mm-DD");
+
 // Helper for AdjustDaysMap.
 void AdjustDay(const std::string &day, int64_t delta,
                std::map<std::string, int64_t> *days) {
@@ -80,9 +83,8 @@ void AdjustDaysMap(int64_t start_time_90k, int64_t end_time_90k, int sign,
   memset(&mytm, 0, sizeof(mytm));
   time_t start_ts = start_time_90k / kTimeUnitsPerSecond;
   localtime_r(&start_ts, &mytm);
-  const char kFmt[] = "%Y-%m-%d";
-  char buf[sizeof("YYYY-mm-DD")];
-  strftime(buf, sizeof(buf), kFmt, &mytm);
+  char buf[kDayFmtBufSize];
+  strftime(buf, sizeof(buf), kDayFmt, &mytm);
 
   // Determine the start of the next day.
   // Note that mktime(3) normalizes tm_mday, so this should work on the last
@@ -106,7 +108,7 @@ void AdjustDaysMap(int64_t start_time_90k, int64_t end_time_90k, int sign,
   }
 
   // Fill |buf| with the second day.
-  strftime(buf, sizeof(buf), kFmt, &mytm);
+  strftime(buf, sizeof(buf), kDayFmt, &mytm);
 
   // Adjust the second day.
   auto second_day_delta = sign * (end_time_90k - boundary_90k);
@@ -117,6 +119,30 @@ void AdjustDaysMap(int64_t start_time_90k, int64_t end_time_90k, int sign,
 
 }  // namespace internal
 
+bool GetDayBounds(const std::string &day, int64_t *start_time_90k,
+                  int64_t *end_time_90k, std::string *error_message) {
+  struct tm mytm;
+  memset(&mytm, 0, sizeof(mytm));
+  if (strptime(day.c_str(), kDayFmt, &mytm) != day.c_str() + day.size()) {
+    *error_message = StrCat("Unparseable day: ", day);
+    return false;
+  }
+
+  mytm.tm_isdst = -1;
+  mytm.tm_hour = 0;
+  mytm.tm_min = 0;
+  mytm.tm_sec = 0;
+  *start_time_90k = kTimeUnitsPerSecond * static_cast<int64_t>(mktime(&mytm));
+
+  mytm.tm_isdst = -1;
+  mytm.tm_hour = 0;
+  mytm.tm_min = 0;
+  mytm.tm_sec = 0;
+  ++mytm.tm_mday;
+  *end_time_90k = kTimeUnitsPerSecond * static_cast<int64_t>(mktime(&mytm));
+  return true;
+}
+
 bool MoonfireDatabase::Init(Database *db, std::string *error_message) {
   CHECK(db_ == nullptr);
   db_ = db;
diff --git a/src/moonfire-db.h b/src/moonfire-db.h
index aed7f65..5640c6b 100644
--- a/src/moonfire-db.h
+++ b/src/moonfire-db.h
@@ -259,6 +259,12 @@ class MoonfireDatabase {
   std::map<int64_t, VideoSampleEntry> video_sample_entries_;
 };
 
+// Given a key in the day-to-duration map, produce the start and end times of
+// the day. (Typically the end time is 24 hours later than the start; but it's
+// 23 or 25 hours for the days of spring forward and fall back, respectively.)
+bool GetDayBounds(const std::string &day, int64_t *start_time_90k,
+                  int64_t *end_time_90k, std::string *error_message);
+
 namespace internal {
 
 // Adjust a day-to-duration map (see MoonfireDatabase::CameraData::days_)