I hate posting these last-minute type of questions, but I'm curious what the setiquette is for this type of situation. It'll probably come in handy to know for the future, as well.

Met a girl (kclose) on Thursday, we made plans to meet up today (Sunday) at 3 to watch the game. Didn't text her again until today around 10AM (we texted Thursday), and haven't gotten a response back. We spent a lot of time together Thursday, and there was solid attraction, so I think this number is pretty solid - I'm surprised by the apparent flake.

There's someone else I'd like to see today, but I don't want to be a dick and ditch plans with the first girl. So my question is: at what point (an hour before? half an hour before? half an hour after?) is it officially deemed a flake, and becomes acceptable to make alternate plans?