I've found it useful to have regularly scheduled estimating meetings. For two-week sprints I hold estimating in the middle of the sprint in the same time-slot as planning. If planning is every other Monday at 10, estimating is the other every other Monday at 10. (Planning is usually longer, though. Planning usually takes one to four hours, depending on the local situation at my client. Estimating usually takes less than one to two hours, depending on how many stories we feel the need to estimate.) Being careful to not let this become waste, we don't estimate more than necessary just because we have a regular meeting.
But why the standing meeting? Why not just estimate whenever needed? The scheduled meeting disrupts the team less than an impromptu meeting. This is because the team knows it's coming and they plan their day around it. This also affords a bit of discipline that even mature teams can benefit from. It forces the product owner to always be ready to estimate and to always have something ready for planning.
This brings me to pre-planning and pre-pointing meetings. I schedule a standing meeting to occur a couple days before each planning day and each estimating day. For newer Product Owners, this is time for the Product Owner to work with the Scrum Master or Agile Coach (me) to be sure the PO is ready. We don't want to come unprepared and waste everyone's time. Many Product Owners continue to use this time in this way even after our engagement is over. When useful, we pull other team members into our prep to help define acceptance criteria or to split stories.
Regular or Impromptu? What do you do?
