I've found that I can type "estimation 30m" to set 30 minutes on the currently selected tasks. However, as I work through my stories and try to estimate the tasks, I usually go down one by one at a time and it would be really helpful to just hit ctrl+E or something simple to set focus to estimation field, then type "30m" and enter.
Edit: Actually, if "est" was sufficient to type as an alternative to "estimation" in command window then that might be just as good as a custom hotkey for it.
Edit: I now found that I can type "e", then hit tab to complete, then "30m". This is a pretty good solution, the only drawback is a small delay before the autocomplete kicks. If "e" or "est" were hard coded shortcuts that would be slightly better, but not a big deal.