3 files changed, 35 insertions, 0 deletions
diff --git a/docs/ref/SUMMARY.md b/docs/ref/SUMMARY.md
index d6663a78..c994ecd5 100644
--- a/docs/ref/SUMMARY.md
+++ b/docs/ref/SUMMARY.md
@@ -12,6 +12,7 @@
 
     - [nng_alloc](./api/util/nng_alloc.md)
     - [nng_clock](./api/util/nng_clock.md)
+    - [nng_duration](./api/util/nng_duration.md)
     - [nng_id_map](./api/util/nng_id_map.md)
     - [nng_msleep](./api/util/nng_msleep.md)
     - [nng_opts_parse](./api/util/nng_opts_parse.md)
diff --git a/docs/ref/api/util/index.md b/docs/ref/api/util/index.md
index 0650c21d..0a3cb891 100644
--- a/docs/ref/api/util/index.md
+++ b/docs/ref/api/util/index.md
@@ -7,6 +7,7 @@ of other uses.
 
 - [nng_alloc](nng_alloc.md) --- allocate memory
 - [nng_clock](nng_clock.md) --- get time
+- [nng_duration](nng_duration.md) -- relative time in milliseconds
 - [nng_id_map](nng_id_map.md) --- identifier based mapping table
 - [nng_msleep](nng_msleep.md) --- sleep milliseconds
 - [nng_opts_parse](nng_opts_parse.md) --- parse command line options
diff --git a/docs/ref/api/util/nng_duration.md b/docs/ref/api/util/nng_duration.md
new file mode 100644
index 00000000..9ad76256
--- /dev/null
+++ b/docs/ref/api/util/nng_duration.md
@@ -0,0 +1,33 @@
+# nng_duration
+
+## NAME
+
+nng_duration --- relative time in milliseconds
+
+## SYNOPSIS
+
+```c
+#include <nng/nng.h>
+
+typedef int32_t nng_duration;
+
+#define NNG_DURATION_INFINITE (-1)
+#define NNG_DURATION_DEFAULT  (-2)
+#define NNG_DURATION_ZERO     (0)
+```
+
+## DESCRIPTION
+
+An {{i:`nng_duration`}}{{hi:duration}} is a relative time, measured in {{i:milliseconds}}.
+This type is most often used in conjunction with timers and timeouts.
+
+A couple of special values have been set aside, and carry special meanings.
+
+- {{i:`NNG_DURATION_DEFAULT`}}:
+  Indicates a context-specific default value should be used.
+
+- {{i:`NNG_DURATION_INFINITE`}}:
+  Effectively an infinite duration; used most often to disable timeouts.
+
+- {{i:`NNG_DURATION_ZERO`}}:
+  Zero length duration; used to perform an immediate poll.