[danpker]

It provides the right output if the right timezone is given:

http://www.wolframalpha.com/input/?i=hours+between+1pm+est+m...

[chrisrhoden]

http://www.wolframalpha.com/input/?i=hours+between+1pm+est+m...

[arundelo]

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.