I've been working with Android ever since it came into the market, and with Java for 12 years now. An app like this is a walk in the park - I doubt I would need half of the time I requested (10 days).
For this project, I plan to first get the design work out of the way; I'll get it to look the way you want it to look like, and then I'll implement functionality. I'll end up using an Excel API to read the spreadsheet, and have default column names that it'll look for (so for example, it'll look for "Name" and "Birthday", but if they aren't there, it'll let the user match up column names with data values so there would be no issues with spreadsheet compatibility.) After that, it's merely scheduling the messages for sending, and making sure that the app continues to send messages even after phone restarts.
I'm highly interested in this project and would love to see it come to life. Please, don't hesitate to contact me either through Skype or from my email. I look forward to hearing from you.