updated system.time vs now notes

content/v2.0/reference/flux/stdlib/built-in/misc/now.md

@@ -30,6 +30,11 @@ data
 {{% note %}}
 #### now() vs system.time()
 `now()` returns the current UTC time.
+`now()` is cached at runtime, so all instances of `now()` in a Flux script
+return the same value.
+
 [`system.time()`](/v2.0/reference/flux/stdlib/system/time/) returns the current
 system time of the host machine, which typically accounts for the local time zone.
+This time represents the time at which `system.time()` it is executed, so each
+instance of `system.time()` in a Flux script returns a unique value.
 {{% /note %}}

content/v2.0/reference/flux/stdlib/system/time.md

@@ -37,5 +37,10 @@ data
 #### system.time() vs now()
 `system.time()` returns the current system time of the host machine, which
 typically accounts for the local time zone.
+This time represents the time at which `system.time()` it is executed, so each
+instance of `system.time()` in a Flux script returns a unique value.
+
 [`now()`](/v2.0/reference/flux/stdlib/built-in/misc/now/) returns the current UTC time.
+`now()` is cached at runtime, so all instances of `now()` in a Flux script
+return the same value.
 {{% /note %}}