(If anyone does want to build an extension for Buffer, I'd love something that let me schedule certain tweets to post on certain dates way off in the future.. but I don't want to sign up to Hootsuite or anything big like that.)
But anyways, it would be pretty easy to add this feature to Tampon. I've been thinking about it actually!
Not to dilute your efforts at all, but something like "Buffer-like app" or "Buffer-style app" or "Buffer-esque app" would be more precise.
Anyway, congrats for doing this. Back when Buffer's pricing plan was horrible, I was almost tempted to do something similar. Since their reorganization, I've been happy with their pricing plan, but it's always great that open alternatives exist.
A "Buffer" is pretty generic in software though, so this wording might be confusing also. You could say RabbitMQ is an open source buffer as well :)