Most Helpful Girl
Since you and your girlfriend are both pretty busy, I'd set it up early, just so she knows you want to hang out.
Then a few days before the date, check with her again to make sure nothing's changed and you're both still free that day
Most Helpful Guys
Depends where you are in the relationship, how good your communication is and what you are both comfortable with. I generally do that with my girlfriend.
I wouldn't. It seems too structured. I also prefer to live spontaneously though so that situations don't get stale and relationships grow organically.