Hi Chris,
Like Justin says, limiting yourself to 800 fetches per script execution will work for one account. However, this 20,000 fetch limit per day applies per-user (i.e. per-login-email), not per-script. If you've got multiple scripts doing URL fetches, they're both eating up the same quota. What you could do to work around this is to check fewer links per script execution, or maybe have another user schedule the script on the other account.