- There could be a security issue for which an urgent patch needs to be released,
- There could be some new feature that is meant to be pushed through before the next release
- Because the release schedule is long, defects that are found during the next few months are collected and released in an interim release that is then released
- And this is one of the most interesting reasons for a release - I know several people who will not take a new version of a Microsoft until a service pack has been released, since that is when it would have stabilized - so this puts pressure on a company to do a release within a few months
With all this, who does these interim releases ? For products where there is already a definite schedule of interim releases, a small sub-team can be setup to take care of these releases. Such a team will soon gain expertise in doing these smaller releases, and can work on the main release if there are no interim releases ongoing. However, for teams where there is no definite schedule of release of these interim releases, it does not make sense for a team to put dedicated folks to work on the product. Even more, in my experience, when people are assigned to such interim releases, there is a need to rotate the people working on such releases, since these are seen as essential but maintenance, not with the excitement of working for something new.
Now, once people are assigned to do the project, there is a need to figure out the schedule for such a release. However, in most of these cases, the end date is already fixed - the Product Manager already has a date in mind about when these releases need to be released. But, the team still need to define the estimate and a probable schedule in mind:
- Whether this be a dot release or a patch (a patch is a small set of files that is downloaded and can be installed, a dot release is typically the full installer with a few changes in the files). The advantage of having a dot release is that it can replace the original installer
- Define the change that is happening (this typically means the files and features that are being changed, and the estimated impact of this change)
- The amount of time needed for the development team to make the required changes
- The amount of time needed for the testing team to test the area and surrounding areas (this would also include the installer created for the release)
- Typically most products have language versions, and those need to be created and tested when a dot release or a patch is made. So, the estimate for the amount of time needed for these activities also need to be incorporated into the schedule.
Together, all of these can be woven into a schedule for the interim release. If it turns out that the deadline given is less than the projected schedule end, then you need to push back. For a small release, it is next to impossible to meet the project with the required quality principles, unless sufficient time is given. We once had a situation where a particular variation in the installer made a small error in the registry, which then prevented those who installed from being able to install another update, and there was a lot of backlash over that - we had to release another patch for that one.
Read more about the estimation done by a senior member of the development team.