I mean 8:20 is the local time and it tells me the time in New York when it is 8:20 local time. Adding dates could take into account daylight saving...
timein New York at 16:30 on 12/5/2013
Would mean "when it is 16:30 on 12th May 2013 local time, what time would it be in New York".
I guess if you wanted to support conversions to local time you could use a different keyword...
localtime New York at 16:30
Would mean "what is the local time when it is 16:30 in New York"