allow stop times with same times for flex

lib/editor/selectors/timetable.js

@@ -157,6 +157,7 @@ const isCellValueInvalid = (
   tripIds: Array<string>
 ): ?EditorValidationIssue => {
   const col = columns[colIndex]
+  const isFlexInvolved = columns.some(isFlexStopTime)
 
   if (isTimeFormat(col.type)) {
     // FIXME: This does not yet support validating frequency start/end times.
@@ -176,7 +177,7 @@ const isCellValueInvalid = (
       // Ensure value is increasing over previous value
       // Flexible stop times (because intra zonal trips are represented by a duplicate stop time) can
       // include the same start and end pickup times back to back and so must avoid this check.
-      const isInvalid = !isFlexStopTime(col) && val < previousValue
+      const isInvalid = !isFlexInvolved && val < previousValue
       return isInvalid
         ? {
           field: col.key,