diff --git a/doc/arch/sandbox.rst b/doc/arch/sandbox.rst
index 1a7801a..60ee1e0 100644
--- a/doc/arch/sandbox.rst
+++ b/doc/arch/sandbox.rst
@@ -131,6 +131,13 @@
 -i
   Go to interactive mode after executing the commands specified by -c.
 
+Environment Variables
+---------------------
+
+UBOOT_SB_TIME_OFFSET
+    This environment variable stores the offset of the emulated real time clock
+    to the host's real time clock in seconds. The offset defaults to zero.
+
 Memory Emulation
 ----------------