Facebook login is a dead stop for me too. Maybe your demographic is the Facebook generation, but there are lots of non-Facebook generation people who use email, want reminders, have busy lives, and money.
You pick it from the list and I use it to calculate the difference between the current time in your zone and the time you want the message, then add the difference to GMT time on my server. It was simple once I got the dots connected and figured out PHPs DateTime class. :)
Bottom line is I want this thing dead-simple, but this shouldn't add too much overhead, I suppose.