rdisp/async_dialog_timeout is a SAP Parameter attribute which is used to control timeout for asynchronous dialog RFCs information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
This parameter configures the timeout for the structure of an 'Online'
connection between asynchronous RFC servers and the related SAP GUI. An
'online' connection of this type is needed when the application executed
by the RFC server wants to run a dialog with the user. Since the work
process is blocked while setting up the connection, the duration of the
connection setup is restricted.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.