It provides the right output if the right timezone is given:
http://www.wolframalpha.com/input/?i=hours+between+1pm+est+m...
Re:I am disappoint, Wolfram Alpha
by chrisrhoden on Monday March 12, 2012 @11:18AM
(#3693810)
I see 24 hours (not the correct 23) when I follow that link.
Edit: Now I see that the link has both times in EST, which is not on point. See chrisrhoden's link in a sibling to this comment.
Re:I am disappoint, Wolfram Alpha
by chrisrhoden on Monday March 12, 2012 @11:15AM
(#3693797)
A move between non-DST and DST is considered a time zone change - in my case from EST to EDT.
This time zone change is listed there. It says 1:00pm EST to 1:00pm EDT on the page linked, and so it is incorrect.
What is changing is your time zone from, say, GMT to BST.