The key to a good training is preparation. General rule of thumb says, when preparing a standard training you should spend around 3 hours of preparation for 1 hour of training. And this just covers the average case, while if you are new to a given training topic or the topic is rather complex, the time spent can increase drastically.
But what is considered preparation? The preparation can include communicating to your clients and/or participants, drafting the training outline, arranging the logistics, creating/updating the training materials, etc. If we take the mentioned formula, for a one day training workshop a good preparation would take 2-3 days. Can all these elements of preparation fit in such a short time?