Hello,
incoming RFC call is started everytime in a dialog work process on the destination system (if it's SAP system), I suppose that's the reason why you get the timeout dump - because on dialog work process there is the same timeout limit as for the "other" dialog users, see related parameter on destination system (name of the parameter is in the dump - rdisp/max_wprun_time).
Why are you starting the data gabbing by RFC, is it really distant system? If you take it from top view, it's really strange to keep the call alive for e.g. 20 minutes, maybe you should change application design if it is possible (request data in packages, grab data on destination system in background process and send them by rfc..)...
Note that the processing time can be "zeroed" by commit work.
Br
Bohuslav