Each script you create can have a different check frequency depending on how frequently you want that script to run.
Paying accounts can use High Frequency scripts which allow you to select that the script runs continuously, every 15 minutes, every 4 hours, every 8 hours ora daily. Free accounts are limited to using only Low Frequency Scripts which run every 4 hours, 8 hours or daily.
If you are on a paying account, you will have a limited number of High Frequency Scripts. These scripts are ones that have a check frequency of less than 4 hours.
To change the frequency of your script, from your dashboard view the site that has the script, then edit the script and select the new frequency from the "Check Every" select box.
Once you press the "Finish Editing" button, your script will be updated immediately.