# Command Scheduler

Certain commands (e.g., [backup interval](https://docs.islandrouter.com/island-router-cli-2.3.2/commands/backup/backup-interval)) cause an action to occur at regular intervals. In most cases, the start time is not specified by the user, but is calculated by the system. In those cases, the actual clock times for command execution are calculated based on midnight (local system time) on the day the command was issued. For intervals of one week or greater, the times are calculated based on midnight (00:00) Wednesday.

Examples:

<table><thead><tr><th width="149">Interval</th><th>Actual Execution Times</th></tr></thead><tbody><tr><td>4 hours</td><td>00:00, 04:00, 08:00, 12:00, 16:00, and 20:00 each day</td></tr><tr><td>18 hours</td><td>00:00 and 18:00 on the first day and 12:00 on the second day</td></tr><tr><td>36 hours</td><td>00:00 on the first day and 12:00 on the second day</td></tr><tr><td>9 days</td><td>Every 9 days starting at 00:00 on Wednesday</td></tr></tbody></table>