The number of stacks of HM is not shown on the icon (you could estimate it though), but the good news is the server knows how many stackson HM are there and calcs accordingly. When I was playing my hunter I got many new damage records
.
The UI guys know the display problem and are working on it.
DoTimer or similar mods will tell you when the 2 minute timer is about to end, but I think that is all you can do for now.