I was recently asked if it was ok to do the Sprint Retro on Sprint Planning day…

The most obvious answer to this question is that the team have broken the timebox of the Sprint. The Sprint has been extended by half a day to accommodate the Retro. This is a ScrumBut (We do Scrum but we do the Retro on Planning day by extending the Sprint by half a day) Scrum anti-pattern:

This is a good round-up on not extending Sprints:

Another view from a more traditional PM viewpoint:

“Working in timeboxes is equal to creating short milestones and achieving those milestones in a continuous manner.

The reason for this we can understand through the Temporal Motivation Theory. This theory (TMT) was developed by Piers Steel and Cornelius J. Konig. The theory emphasizes time as a critical, motivational factor. The Temporal Motivation Theory formula can be applied to human behavior, procrastination, and to goal setting. According to Lord, Diefenforff, Schmidt, and Hall, the theory models the motivating power of approaching deadlines, arguing that the perceived utility of a given activity increases exponentially as the deadline nears.”

So there you go…quote Temporal Motivation Theory. Timeboxing is science