I'm using the reminders plugin for my 3.0 setup. I've got a "Abandoned Cart" reminder setup to send after 12 hours, but I get the email after just a few minutes of adding an item to my cart.
Here's a screen shot of my setup:
It looks like your setup is not correct. If you want to send the first reminder only after 12 hours since the shopping cart item has been added then you should set the "Condition Met Date Earlier Than:" to be 12 hours (your current one is empty, which defaults to 0 minutes). You should also set the "Condition Met Date Later Than:" to be something like 5 days for example, which means that any customer with a shopping cart item that has been added 5 days ago won't be bothered with reminders.
I think the names of the settings are a bit confusing and unclear, so any suggestions of changing them are welcome.