diff --git a/modules/time_utils.js b/modules/time_utils.js
index 152de2fd0..5ca153710 100644
--- a/modules/time_utils.js
+++ b/modules/time_utils.js
@@ -1,54 +1,78 @@
 // module "time_utils"
 //
 // Utility functions useful to work with time and durations.
-// Functions usually receive or return a {h, m} object or a
-// number of milliseconds representing a time or a duration.
+//
+// This module functions usually receive or return a {d, h, m, s} object
+// or a number of milliseconds representing a time or a duration.
+//
+// The {h, m, s} object encapsulates a "time" (eg: 12:30:00).
+// Note: a "time" needs the day set to 0/undefined, otherwise it is a "duration".
+//
+// The {d, h, m, s} object encapsulates a "duration" in number of days, hours,
+// minutes and seconds (eg. 3d 20h 35m 20s).
+// Note that if a field is undefined then its value is zero.
 //
 
+const ONE_SECOND = 1000;
+const ONE_MINUTE = 60 * ONE_SECOND;
+const ONE_HOUR = 60 * ONE_MINUTE;
+const ONE_DAY = 24 * ONE_HOUR;
+
 /**
- * @param {object} time {h, m}
+ * @param {object} time {d, h, m, s}
  * @returns the milliseconds contained in the passed time object
  */
-exports.encodeTime = (time) => time.h * 3600000 + time.m * 60000;
+exports.encodeTime = (time) => {
+  time = safeTime(time);
+  return time.d * ONE_DAY + time.h * ONE_HOUR + time.m * ONE_MINUTE + time.s * ONE_SECOND;
+}
+
+// internal use, set to zero all the undefined fields
+function safeTime(time) {
+  return { d: time.d || 0, h: time.h || 0, m: time.m || 0, s: time.s || 0 };
+}
 
 /**
  * @param {int} millis the number of milliseconds
- * @returns a time object {h, m} built from the milliseconds
+ * @returns a time object {d, h, m, s} built from the milliseconds
  */
 exports.decodeTime = (millis) => {
-  millis = Math.ceil(millis / 60000);
-  var h = 0 | (millis / 60);
-  return {
-    h: h,
-    m: millis - h * 60
-  };
+  if (typeof millis !== "number") throw "Only a number can be decoded";
+  var d = Math.floor(millis / ONE_DAY);
+  millis -= d * ONE_DAY;
+  var h = Math.floor(millis / ONE_HOUR);
+  millis -= h * ONE_HOUR;
+  var m = Math.floor(millis / ONE_MINUTE);
+  millis -= m * ONE_MINUTE;
+  var s = Math.floor(millis / ONE_SECOND);
+  return { d: d, h: h, m: m, s: s };
 }
 
 /** 
- * @param {object|int} value {h,m} object or milliseconds
+ * @param {object|int} value {h, m} object or milliseconds
  * @returns an human-readable time string like "10:25"
+ * @throws an exception if d != 0 or h > 23 or m > 59
  */
 exports.formatTime = (value) => {
-  var time = (value.h === undefined || value.m === undefined) ? exports.decodeTime(value) : value;
+  var time = safeTime(typeof value === "object" ? value : exports.decodeTime(value));
+  if (time.d != 0) throw "(d)ays not supported here";
+  if (time.h < 0 || time.h > 23) throw "Invalid value: must be 0 <= h <= 23";
+  if (time.m < 0 || time.m > 59) throw "Invalid value: must be 0 <= m <= 59";
   return time.h + ":" + ("0" + time.m).substr(-2);
 }
 
 /**
- * @param {object|int} value {h,m} object or milliseconds
- * @returns an human-readable duration string like "1h 10m"
+ * @param {object|int} value {d, h, m, s} object or milliseconds
+ * @returns an human-readable duration string like "3d 1h 10m 45s"
  */
 exports.formatDuration = (value) => {
-  var duration;
-
-  var time = (value.h === undefined || value.m === undefined) ? exports.decodeTime(value) : value;
-
-  if (time.h == 0) {
-    duration = time.m + "m"
-  } else {
-    duration = time.h + "h" + (time.m ? (" " + time.m + "m") : "")
-  }
-
-  return duration
+  var duration = "";
+  var time = safeTime(typeof value === "object" ? value : exports.decodeTime(value));
+  if (time.d > 0) duration += time.d + "d ";
+  if (time.h > 0) duration += time.h + "h ";
+  if (time.m > 0) duration += time.m + "m ";
+  if (time.s > 0) duration += time.s + "s"
+  return duration.trim();
 }
 
 exports.getCurrentTimeMillis = () => {