I think all speculations about using the random generator of the servers will fail...
OK, let's say that you are able to find an interval which gives you the right random number always
BUT...
It only works, if you are sitting behind a server machine. If not, you must calculate with the time for traffic flow throuht network.
The random generator is based on less than milisec. interval, and the latency of pings is more than a milisecond.
Just try to ping the server address, you will get different values.maybe 10-20-100 pings same, but allways will be one which can delay your enchant request, and this is the point where the enchanted item broke