Use Time enumeration

src/enums/Time.js

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+// SPDX-FileCopyrightText: 2021 Romain Vigier <contact AT romainvigier.fr>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+/**
+ * Time is an enumeration of the possible time values.
+ */
+var Time = {
+    UNKNOWN: 'unknown',
+    DAY: 'day',
+    NIGHT: 'night',
+};