docs on time

docs/scarpet/language/SystemFunctions.md

@@ -263,8 +263,11 @@ sleep(50)
 
 ### `time()`
 
-Returns the number of milliseconds since 'some point', like Java's `System.nanoTime()`. 
-It returns a float, which has 1 microsecond precision (0.001 ms)
+Returns the number of milliseconds since 'some point', like Java's `System.nanoTime()`, which varies from system to 
+system and from Java to Java. This measure should NOT be used to determine the current (date)time, but to measure
+durations of things.
+it returns a float with time in milliseconds (ms) for convenience and microsecond (μs) resolution for sanity.
+
 
 <pre>
 start_time = time();