Displaying a scheduled job under a scheduled time
Your script creates a temporary file unnecessarily, uses os.system which is not recommended, and other messy things. Consider this alternative:

#!/usr/bin/env python

import subprocess
import re

re_job_number = re.compile(r'\d+')

for atq_line in subprocess.Popen(['atq'], stdout=subprocess.PIPE).stdout:
    job_number = re_job_number.search(atq_line).group()
    print atq_line.strip()
    for at_line in subprocess.Popen(['at', '-c', job_number], stdout=subprocess.PIPE).stdout:
        if at_line.startswith('task '):
            print at_line.strip()
    print '-' * 40


Advantages:


No need for a temporary file to save the atq output, you can process it directly
For running shell commands, subprocess is the recommended way, os.system is discouraged
No need for a grep process, you can handle the output filtering of at -c in Python itself


Also, writing the first line this way makes the script more portable:

#!/usr/bin/env python


If you write as #!/usr/bin/python then you are effectively hard-coding the Python path, and it might not be the same in all systems.

Finally, I recommend writing print(something) instead of print something, to keep your script ready for migrating to Python 3 someday.