We’ve known for a few weeks now that the Sprint HTC Hero would probably be getting the bumpgrade up to Android 2.1 sometime in April — but really, was anyone expecting the launch window rumor to stay that vague?

Phandroid just dug up this alleged internal Sprint memo, detailing a “maintenance release” coming to the HTC Hero on April 9th. While “maintenance release” makes it sound like something trivial, that’s probably not the case. Sprint tends to be pretty intense about certification, spending weeks testing out updates before they release them. It seems pretty unlikely that they’d release a minor update just days before the major update to 2.1.

Go ahead, Sprint Hero owners: sit on the edge of your seat. If this all plays out right, you probably won’t be there much longer.