New reshape2 question

You shouldn't need to worry about your system clock (time)  for analyzing time data from files, but only your system timezone. The default value of TZ leads to assuming system timezone... setting it explicitly changes the assumed timezone for the purposes of the current instance of R. 
I prefer to keep the conversation on list so others can chime in or learn from the exchange or correct my mistakes.
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Jeff Newmiller                        The     .....       .....  Go Live...
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Sent from my phone. Please excuse my brevity.

Tnx Jeff,

I will work through your suggestions.
The time zone is actually in Chile and not U.S. time zones.

The use of POSIXt is something I need to get up to speed with.
It may make more sense ecologically to combine the dates and times then

summarize into 15 minute time blocks.  I will need to read carefully
how 
to avoid using my workstation system clock in doing this for data 
conversions of times from other time zones.

Bruce