automatic deactivation of substitution in workflow

Hi Experts,

I have fully customized the program rmps_set_substitute as per my requirement.in that development, i have customized standard function modules..RH_SET_SUBSTITUTE_DELETE  and RH_SET_SUBSTITUTE_CUT to get original work items back to the original user(which are processed by substitute user) in delete and delemet buttons.

but now that custom development has to be applicable when automatic deactivation occures also.

example.

original user      sub-user    begin date            end-date

A                           B           30.07.2015       31.07.2015.

When i check on 01.08.2015 the substitution will be automatically deactivated.we can see in rmps_set_substitution transaction.

how it is deactivated..where it is happening in the program..is there any back ground job running.?

Kindly let me know.

Regards,

Ramesh.