Doing multiple workings is fine as long as you're not spreading your energies too thin and feeling drained constantly. If that happens all of your workings will suffer.
Besides what power of justice said, it is also important that you can keep your focus on the working you are doing. Longer and more vibrations will also amplify your workings, having multiple workings to balance can really lower the quality of the workings. Only do this when you are comfortable enough to do so.