I asked about a way to specify a time when using org-resolve-clock instead of a number of minutes:
I've implemented this myself and a patch is attached. Comments welcome -- my change works, but I'm not sure about coding style, and right now there's no error checking.
I marked the patch as a tiny change, but it does add a new menu option and behavior to org-resolve-clock, so there may be an argument that it's not, from a user perspective, a "tiny change", but code-wise it's quite simple: the core logic really isn't more than "ask the user for a time and subtract".
I hope this change can be incorporated into the official Org release.
Ceci n'est pas une .signature.