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

The answer depends on context. Many teams find it most efficient to do all the Scrum events on 1 day e.g. Review/Retro/Planning. If that is agreed up-front as part of teams normal cadence that is fine. However if the Sprint has been extended by half a day to accommodate the Retro, for example the Retro is planned for a Friday afternoon (on a Mon-Fri sprint) and it is moved to Monday morning, then this is a ScrumBut anti-pattern. (We do Scrum but we do the Retro on Planning day by extending the print by half a day):

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