The browser Synchronization timeout is set to 60 seconds and the object synchronization timeout to 20 seconds...but whatever these values be since i have given 75 seconds in the waitproperty it should override all these things. If not then there is no use of waitproperty.
WaitProperty presumes that the object exists, just not in the desired state. As in the example given in help of checking for the text "Ready", in a static control. If you just want to see if it loads use .exist or run a loop using GetRoProperty for the enabled/visible attribute.
Reserve WaitProperty usage for checking state changes.