If you can generate an RSS feed to supply the tweets, IFTTT will spit them out on Twitter around every 15 minutes.
There's also a pretty cool self hosted PHP application called Twando. It's free, open source, and will let you upload a CSV of as many tweets as you want and what time to send them. You'll have to do a little work installing it on a server and setting up cron jobs, but it's pretty sweet software actually.