On sched II's there's no leeway...you can't fill before the date of the script...and must be filled within 7 days of being written...on sched III's there is some pharmacist discretion....usually it's a percentage formula.....like when you've reached 80% of the prescribe dose...you can refill...but can depend on your insurance & YOUR OWN PERSONAL HISTORY. If you have a HISTORY of asking for your schedule III's early every month..the pharmacist can refuse to fill before 30 days...
I've found it's best to establish a long term relationship with a specific pharmacist at a pharmacy & deal only with them....find out when they work & use them, be kind, be appreciative of their assistance & they'll be as lenient as they can....