I tried to set a timestamp "thu 12:00+1.5", using C-c . and typing the
characters in quotes.  What I got was
<2010-08-12 Thu 12:00-13:00>

I found that 12:00+1:30 works fine, but it seems like 1.5 should be
parsed.

Separately, I'd like 24-hour time without colons to work.  "thu 1400"
seems unambiguous, but just shows up as thursday without a time.

I don't know how hard these are or if there are reasons not to, but I
thought I'd throw out the idea.