add recipe

Author: Vinh Nguyen

docs/basics/index.md

@@ -7,3 +7,7 @@ Back to [Main](../../README.md)
 ## Lang
 
 - [String](lang/String.md)
+
+## Time
+
+- [OffsetDateTime](time/OffsetDateTime.md)

docs/basics/time/OffsetDateTime.md

@@ -0,0 +1,11 @@
+# OffsetDateTime
+
+## Convert to Millis
+
+Use `Instant` to get epoch milliseconds.
+
+```java
+OffsetDateTime hostTimestamp;
+
+hostTimestamp.toInstant().toEpochMilli();
+```