Man, when I was on reserve, I called nearly every day to be released early from both RAP and standby. I commute but it's an easy one to commute daily from so there were a lot of times where going home just for the night made sense by being released a few hours early.

Anyway, standby is definitely harder to get out of than RAP, but not impossible.

Don't worry about pushing your luck or feeling cheaky about calling too early. Just call and ask. Worst thing is that they say 'no'. If it really is too early, when you call later for the next flight option, they'll remember you really wanted to get out of dodge earlier. Best case, you're released the first time you called. There is no penalty for asking.

If it's your last day, whether you're on standby or RAP, if they hesitate about releasing you, ask them if there are any turns left you're good for and remind them it's your last day. My experience, just them knowing it's your last day is often enough and it's not always obvious to them that it's your last day.

Be nice and courteous on these calls. Don't pick a fight. When they remember you from the last time they talked to you, you don't want them expecting a confrontation.