There are two situationss for leap second adjustment.
1) When the system clock moves forward due to leap second adjustment
This is not an issue for shareplex, capture continues to process.
2) When the system clock moves backward due to leap second adjustment
Capture process is in an idle state for duration of time change after the time change occurs
When SharePlex starts, capture inherits the system time and compares it with the database transaction time before processing. The SharePlex parameter SP_OCT_REDOLOG_ENSURE which by default is enabled (set to 2) ensures that the capture process never gets ahead of Oracle by ensuring that capture is always 2 seconds behind oracle.
During the leap time change when the system clock gets set back n seconds, the capture process compares the system time with the transaction time and as they are different, capture waits for n+2 seconds before it was processed.
Since the change in time is only few seconds, capture would catch up very soon. It is not required to make any changes to shareplex parameters.