Just updated mine to 7720 from 7712, and it only took a few mins
Strange thing though, I haven't been asked to install an update from HTC yet (been on beta since release); even with forcing an update check through Zune...
Also, found a "bug" already on my HTC HD7... Trying to use maps and it cannot find my location.... Probably due to driver not working properly in this OS update.
But, other than that.... Loads up super quick, the transitions between the metro screen and apps have improved a lot more from "beta 2"; can't wait for my apps to update to use mango at it's full potential