You need one more *

The format is:

1. minute
2. hour
3. day-of-month
4. month
5. day-of-week
6. command

You need one more *

The format is:

1. minute
2. hour
3. day-of-month
4. month
5. day-of-week
6. command

Update

Also if you just put 5 in the first field, your command will only be executed 5 minutes after the full hour. To have it executed every 5 minutes it should be */5