By default, when searching in OpenAtrium, the results shown are from the past 6 months. However, there might be a situation where you want to change this for your users. For example, suppose you wanted to show your users all results from any time? This is an option in the drop-down selector once you've made your search, but it's not default. Here's how to sort that out.
OpenAtrium search is controlled by a view and it uses an exposed filter to allow the user to choose the date range for the search results. We need to edit the search_listing view. Find the filters section, and find the Node: post date filter, which should tell you that it is exposed.
Click the filter to edit it. In the value type section, the value is set to -180 days, which is the 6 month default option. You will need to adjust this value. Simply clear the field entirely to turn the default search from 6 months to any time. You will also see a Remember checkbox, which you can disable to force people to use your new setting. Otherwise, they will continue to use the '6 month' setting if they've used it before.
Note that the value you enter in the value type section must correspond to one of the values specified in the _atrium_form_views_exposed_form_alter() function, found inside atrium.inc inside the profiles/openatrium/modules/atrium_features/atrium directory. In fact, if you wanted to, you could create your own module that implemented the same function, and, providing your module was executed after the OpenAtrium version, you could insert your own values here, such as 1 week, or 5 days. Note while it's possible to edit the OpenAtrium code directly, this is not recommended as it makes upgrading OpenAtrium difficult.