<p> The expression that defines when the schedule runs. The following formats are supported. </p> <ul> <li> <p> <code>at</code> expression - <code>at(yyyy-mm-ddThh:mm:ss)</code> </p> </li> <li> <p> <code>rate</code> expression - <code>rate(value unit)</code> </p> </li> <li> <p> <code>cron</code> expression - <code>cron(fields)</code> </p> </li> </ul> <p> You can use <code>at</code> expressions to create one-time schedules that invoke a target once, at the time and in the time zone, that you specify. You can use <code>rate</code> and <code>cron</code> expressions to create recurring schedules. Rate-based schedules are useful when you want to invoke a target at regular intervals, such as every 15 minutes or every five days. Cron-based schedules are useful when you want to invoke a target periodically at a specific time, such as at 8:00 am (UTC+0) every 1st day of the month. </p> <p> A <code>cron</code> expression consists of six fields separated by white spaces: <code>(minutes hours day_of_month month day_of_week year)</code>. </p> <p> A <code>rate</code> expression consists of a <i>value</i> as a positive integer, and a <i>unit</i> with the following options: <code>minute</code> | <code>minutes</code> | <code>hour</code> | <code>hours</code> | <code>day</code> | <code>days</code> </p> <p> For more information and examples, see <a href="https://docs.aws.amazon.com/scheduler/latest/UserGuide/schedule-types.html">Schedule types on EventBridge Scheduler</a> in the <i>EventBridge Scheduler User Guide</i>. </p>