To add my penny's worth, I am of the opinion that you don't make any firm plans outside of work before your official duty is over. Then if you get an early go its a bonus. If not, you can't be dissapointed.
An early go is a privalage not a right.
I don't think anybody would be-grudge the infrequent request for an early go if you are desperate, but don't be p@s*ed off if the answer is no.
