hat is understood by 
MazamaCoreUtils::parseDatetime(). For non-POSIXct values,
the recommended format is "YYYY-mm-dd HH:MM:SS".
Timezone determination precedence assumes that if you are passing in
POSIXct times then you know what you are doing.

get timezone from startdate if it is POSIXct
use passed in timezone
get timezone from pat

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