24-hour callout is an option that is discussed in section 25.I. Option 2. This is used for the situation when a trip is pulled for IOE or management flying.

You cannot just simply make any given reserve day a 24-hour callout. If you are a commuter, you can call scheduling and request a later start or earlier finish to your awarded contact period in order to make the string of days more commutable. This can be approved at the their discretion, so don't always count on it. When staffing levels are good, they are typically flexible on these start/end times.