We typically recommend between 1 and 2 hours a week. It is always much better to provide your employees a slow, steady, & consistent stream of information over an extended period of time. One hour a week for 40 weeks can be much more effective than one 40-hour week in altering the behavior and improving the skills of your employees.

There is always a place for multi-day training sessions, but they are most effective in teaching a specific skill rather than relaying general knowledge.

-Andy