diff --git a/include/Clock.h b/include/Clock.h
index 2ed163b..80858f6 100644
--- a/include/Clock.h
+++ b/include/Clock.h
@@ -12,11 +12,13 @@
 
 void clock_setup(void);
 
-struct timeval clock_time(void);
+struct timeval clock_now(void);
 
 SNTPError clock_sync(NetworkInterface &net);
 
-const char *clock_timestring(const char *format);
-const char *clock_iso8601string(void);
+const char *clock_timestring(struct timeval time, const char *format);
+const char *clock_iso8601string(struct timeval time);
+
+const char *clock_iso8601string_now(void);
 
 #endif
diff --git a/src/Clock.cpp b/src/Clock.cpp
index 93a1f8c..529012f 100644
--- a/src/Clock.cpp
+++ b/src/Clock.cpp
@@ -10,7 +10,7 @@
 	// mbed reads the RTC at boot, do nothing for now
 }
 
-struct timeval clock_time() {
+struct timeval clock_now() {
 	struct timeval timeval;
 	timeval.tv_sec = time(NULL);
 	timeval.tv_usec = 0;
@@ -28,8 +28,7 @@
 	return SNTPSuccess;
 }
 
-const char *clock_timestring(const char *format) {
-	struct timeval time = clock_time();
+const char *clock_timestring(struct timeval time, const char *format) {
 	struct tm *local_time = localtime(&time.tv_sec);
 
 	static char buffer[64];
@@ -45,6 +44,10 @@
 	}
 }
 
-const char *clock_iso8601string(void) {
-	return clock_timestring("%Y-%m-%dT%H:%M:%S");
+const char *clock_iso8601string(struct timeval time) {
+	return clock_timestring(time, "%Y-%m-%dT%H:%M:%S");
+}
+
+const char *clock_iso8601string_now(void) {
+	return clock_iso8601string(clock_now());
 }
diff --git a/src/main.cpp b/src/main.cpp
index a008a4b..8eb1434 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -49,7 +49,7 @@
 	tr_info("Project Tardis");
 
 	clock_setup();
-	tr_info("The time is %s", clock_iso8601string());
+	tr_info("The time is %s", clock_iso8601string_now());
 
 	mountFilesystem(mainBD, mainFS);
 
@@ -82,13 +82,13 @@
 			NetworkInterface *net = network_interface();
 			tr_info("Syncing clock...");
 			tr_info("The current time is %s",
-				clock_iso8601string());
+				clock_iso8601string_now());
 			SNTPError err = clock_sync(*net);
 			if (err != SNTPSuccess) {
 				tr_err("Failed to sync clock, error %i", err);
 			} else {
 				tr_info("The new time is %s",
-					clock_iso8601string());
+					clock_iso8601string_now());
 			}
 		}
 	}