The OSA method uses Open Space to help create the conditions for a rapid, effective and lasting Agile adoption. Before this can happen, a substantial amount of preparation needs to occur.
One of the most important aspects of preparation is allowing enough time for everyone to consider and process the invitation to meet in Open Space. If this is rushed, then the meeting may not be well attended. People need time to consider the invitation. This includes discussing the invitation with friends and colleagues inside the organization.
For this reason, is recommended that about 45 days of time is provided, so that everyone can consider the invitation, discuss it, and decide what to do. The duration of 45 days is not a strict rule. In general, the more people you invite, the more time you want to allow for them to consider and process the invitation.