diff --git a/lib/std/io/io_formatter_private.c3 b/lib/std/io/io_formatter_private.c3
index 0d638edcf..1e75c1414 100644
--- a/lib/std/io/io_formatter_private.c3
+++ b/lib/std/io/io_formatter_private.c3
@@ -141,7 +141,7 @@ fn void! Formatter.out_substr(&self, String str) @private
 	usz l = conv::utf8_codepoints(str);
 	uint prec = self.prec;
 	if (self.flags.precision && l < prec) l = prec;
-	self.right_adjust(' ')!;
+	self.right_adjust(l)!;
 	usz index = 0;
 	usz chars = str.len;
 	char* ptr = str.ptr;
diff --git a/lib/std/time/datetime.c3 b/lib/std/time/datetime.c3
index 1636b9a61..d56bf6af8 100644
--- a/lib/std/time/datetime.c3
+++ b/lib/std/time/datetime.c3
@@ -133,24 +133,19 @@ fn Time DateTime.to_time(&self) @inline
 	return self.time;
 }
 
-fn bool DateTime.after(&self, DateTime compare)
+fn bool DateTime.after(&self, DateTime compare) @inline
 {
 	return self.time > compare.time;
 }
 
-fn bool DateTime.before(&self, DateTime compare)
+fn bool DateTime.before(&self, DateTime compare) @inline
 {
 	return self.time < compare.time;
 }
 
 fn int DateTime.compare_to(&self, DateTime compare)
 {
-	switch
-	{
-		case self.time > compare.time: return 1;
-		case self.time < compare.time: return -1;
-		default: return 0;
-	}
+	return compare_to(self.time, compare.time);
 }
 
 fn int DateTime.diff_years(&self, DateTime from)
diff --git a/lib/std/time/time.c3 b/lib/std/time/time.c3
index 9c540f680..25a5a47d9 100644
--- a/lib/std/time/time.c3
+++ b/lib/std/time/time.c3
@@ -84,4 +84,71 @@ fn double Time.diff_weeks(time, Time other) => (long)time.diff_us(other) / (doub
 fn double NanoDuration.to_sec(nd) => (double)nd / 1_000_000_000.0;
 fn long NanoDuration.to_ms(nd) => (long)nd / 1_000_000;
 fn TimeDuration NanoDuration.to_duration(nd) => (TimeDuration)nd / 1_000;
-fn NanoDuration TimeDuration.to_nano(td) => (NanoDuration)td * 1_000;
\ No newline at end of file
+fn NanoDuration TimeDuration.to_nano(td) => (NanoDuration)td * 1_000;
+
+fn void! NanoDuration.to_format(&self, Formatter* formatter) @dynamic
+{
+	NanoDuration nd = *self;
+	if (nd == 0)
+	{
+		formatter.printf("0s")!;
+		return;
+	}
+
+	bool neg = nd < 0;
+	if (neg) nd = -nd;
+
+	DString str;
+	str.tinit();
+	if (nd < 1_000_000_000)
+	{
+		// Less than 1s: print milliseconds, microseconds and nanoseconds.
+		NanoDuration ms = nd / 1_000_000;
+		if (ms > 0)
+		{
+			str.printf("%dms", ms);
+			nd -= ms * 1_000_000;
+		}
+		NanoDuration us = nd / 1000;
+		if (us > 0)
+		{
+			str.printf("%dµs", us);
+			nd -= us * 1000;
+		}
+		if (nd > 0)
+		{
+			str.printf("%dns", nd);
+		}
+	}
+	else
+	{
+		// More than 1s: print hours, minutes and seconds.
+		NanoDuration ms = (nd - nd / 1_000_000_000 * 1_000_000_000) / 1_000_000;
+
+		nd /= 1_000_000_000;
+		NanoDuration hour = nd / 3600;
+		if (hour > 0)
+		{
+			str.printf("%dh", hour);
+			nd -= hour * 3600;
+		}
+		NanoDuration min = nd / 60;
+		if (min > 0)
+		{
+			str.printf("%dm", min);
+			nd -= min * 60;
+		}
+		NanoDuration sec = nd;
+		if (ms > 0)
+		{
+			// Ignore trailing zeroes.
+			while (ms / 10 * 10 == ms) ms /= 10;
+			str.printf("%d.%ds", sec, ms);
+		}
+		else
+		{
+			str.printf("%ds", sec);
+		}
+	}
+	formatter.printf(str.as_str())!;
+}
\ No newline at end of file
diff --git a/test/unit/stdlib/io/printf.c3 b/test/unit/stdlib/io/printf.c3
index e506a119c..66feb321f 100644
--- a/test/unit/stdlib/io/printf.c3
+++ b/test/unit/stdlib/io/printf.c3
@@ -2,10 +2,19 @@ module std::io @test;
 
 fn void printf_a()
 {
-	assert(string::printf("%08.2a", 234.125) == "0x1.d4p+7");
-	assert(string::printf("%a", 234.125) == "0x1.d44p+7");
-	assert(string::printf("%A", 234.125) == "0X1.D44P+7");
-	assert(string::printf("%20a", 234.125) == "          0x1.d44p+7");
-	assert(string::printf("%-20a", 234.125) == "0x1.d44p+7          ");
-}
-
+	String s;
+	s = string::printf("%08.2a", 234.125);
+	assert(s == "0x1.d4p+7", "got '%s'; want '0x1.d4p+7'", s);
+	s = string::printf("%a", 234.125);
+	assert(s == "0x1.d44p+7", "got '%s'; want '0x1.d44p+7'", s);
+	s = string::printf("%A", 234.125);
+	assert(s == "0X1.D44P+7", "got '%s'; want '0X1.D44P+7'", s);
+	s = string::printf("%20a", 234.125);
+	assert(s == "          0x1.d44p+7", "got '%s'; want '          0x1.d44p+7'", s);
+	s = string::printf("%-20a", 234.125);
+	assert(s == "0x1.d44p+7          ", "got '%s'; want '0x1.d44p+7          '", s);
+	s = string::printf("%-20s", "hello world");
+	assert(s == "hello world         ", "got '%s'; want 'hello world         '", s);
+	s = string::printf("%20s", "hello world");
+	assert(s == "         hello world", "got '%s'; want '         hello world'", s);
+}
\ No newline at end of file
diff --git a/test/unit/stdlib/time/time.c3 b/test/unit/stdlib/time/time.c3
new file mode 100644
index 000000000..afe6f199c
--- /dev/null
+++ b/test/unit/stdlib/time/time.c3
@@ -0,0 +1,29 @@
+module nanoduration_test @test;
+import std::io;
+import std::time;
+
+fn void! to_format()
+{
+	char[32] buffer;
+	char[] buf;
+	buf = io::bprintf(buffer[..], "%s", (NanoDuration)123)!;
+	assert(buf == "123ns", "got %s; want 123ns", buf);
+
+	buf = io::bprintf(buffer[..], "%s", (NanoDuration)123_000)!;
+	assert(buf == "123µs", "got %s; want 123µs", buf);
+
+	buf = io::bprintf(buffer[..], "%s", (NanoDuration)123_000_000)!;
+	assert(buf == "123ms", "got %s; want 123ms", buf);
+
+	buf = io::bprintf(buffer[..], "%s", (NanoDuration)13_000_000_000)!;
+	assert(buf == "13s", "got %s; want 13s", buf);
+
+	buf = io::bprintf(buffer[..], "%s", (NanoDuration)123_000_000_000)!;
+	assert(buf == "2m3s", "got %s; want 2m3s", buf);
+
+	buf = io::bprintf(buffer[..], "%s", (NanoDuration)12345_000_000_000)!;
+	assert(buf == "3h25m45s", "got %s; want 3h25m45s", buf);
+
+	buf = io::bprintf(buffer[..], "%s", (NanoDuration)12_100_000_000)!;
+	assert(buf == "12.1s", "got %s; want 12.1s", buf);
+}
\ No newline at end of file