Always show at least the most recent valid_time in timeline

lib/microwaveprop/propagation.ex

@@ -121,18 +121,33 @@ defmodule Microwaveprop.Propagation do
     end
   end
 
-  @doc "Returns distinct valid_times for a band from now onward, ordered ascending."
+  @doc """
+  Returns distinct valid_times for a band, ordered ascending.
+  Filters out times more than 1 hour in the past, but always includes
+  the most recent valid_time so there's always data to display.
+  """
   def available_valid_times(band_mhz) do
-    now = DateTime.utc_now() |> DateTime.add(-1800, :second)
+    cutoff = DateTime.utc_now() |> DateTime.add(-3600, :second)
 
-    Repo.all(
-      from(gs in GridScore,
-        where: gs.band_mhz == ^band_mhz and gs.valid_time >= ^now,
-        select: gs.valid_time,
-        distinct: gs.valid_time,
-        order_by: [asc: gs.valid_time]
+    times =
+      Repo.all(
+        from(gs in GridScore,
+          where: gs.band_mhz == ^band_mhz and gs.valid_time >= ^cutoff,
+          select: gs.valid_time,
+          distinct: gs.valid_time,
+          order_by: [asc: gs.valid_time]
+        )
       )
-    )
+
+    if times == [] do
+      # No future times — return the single most recent as fallback
+      case latest_valid_time(band_mhz) do
+        nil -> []
+        t -> [t]
+      end
+    else
+      times
+    end
   end
 
   @doc """