Require contest durations, prefill end times for unfinished puzzles & allow to modify them

app/models/completion.rb

@@ -68,11 +68,7 @@ class Completion < ApplicationRecord
         self.time_seconds = arr[0].to_i
       end
     else
-      if self.contest.duration_seconds.present?
-        self.time_seconds = self.contest.duration_seconds
-      else
-        self.time_seconds = 2 * 3600
-      end
+      self.time_seconds = self.contest.duration_seconds
       self.display_time_from_start = display_time(self.time_seconds)
     end
   end
@@ -82,9 +78,6 @@ class Completion < ApplicationRecord
       self.remaining_pieces = nil
     else
       self.missing_pieces = nil
-      if !self.offline.present?
-        self.display_time_from_start = nil
-      end
     end
   end