If the case is already before the Crown Court, the defendant has been charged. It is not a matter of waiting for evidence to make the case fit to prosecute; there must be that evidence or the case wouldn't be there in Crown Court.
Modern procedure is to get the case into the hands of the Crown Court judge as fast as possible. There is no hearing, other than a very brief one, in the magistrates'court. Once it is in Crown Court there will be a hearing to manage the case; estimates of time, need for witnesses to attend trial, finding a date etc. It may be months after that that the case is heard; it may be very long or complex or witnesses or counsel may not be available, the lists of cases may be full, there may be a number of reasons why it can't be listed soon after arrival in Crown Court