Unless it is heated the tube should be as short as possible.  Unheated tubes will gather condensation which can affect the sample provided to the instrument.

It is best to give the simulator an extra 15 to 30 minutes after it gets to temperature so that the temperature of the entire system has stabilized.

More information about wet bath standards

It is likely that the simulator will leak and provide lower than expected results.

After screwing the top on the simulator, if you cover the GAS OUT port on the simulator with your finger and blow into the IN PORT, you should not see a steady stream of bubbles in the simulator if the head is connected properly. Be careful when you perform this check that you do not blow too hard, as it will create backpressure and can cause simulator liquid to spray out of the ports.

Depending upon the tolerance allowed for the solution, there should be limits on the number of tests or amount of time that the solution should be used.  This limit may also be a function of the type of instrument that you are using and whether the solution is being recirculated.  Refer to your QAP for the proper determination of this limitiation.