I dont understand why do u want to delete clients.
even if you delete clients and if they have valid Sylink.xml they still report to your sepm.
if you want to delete clients which care not connected to your sepm , well there is default 30 days.
if you have uninstalled clients and want to clean it ASAP then set this setting for 1 day
"Delete Clients that have not connected for __ Days"