It is good UI practice to provide progress. German explanation: http://www.usabilitypatterns.info/catalog/patterns/fortschrittsanzeige.html

If one cannot report progress, one should output the expected waiting time. Having a timeout in place, one can use a timer to report progress. Example: timeout 60 seconds, then 60 seconds is 100% and each 6 seconds the progress can be increased by 6/60 = 10%.