SAS system architecture uses numeric variables for representing DATE (days since 1/1/1960) and DATETIME (seconds since same date at midnight) values.
Also, there are various SAS functions to use with these variables for increment/decrement and manipulation, such as INTCK, INTNX.
It's likely your external date/datetime fields must be converted, using a SAS INFORMAT or the INPUT function with a suitable INFORMAT.
Suggest you may also want to search the SAS forum archives as well as using the SAS support http://support.sas.com/ website where there is SAS-hosted documentation and supplemental technical / conference materials (extensive) on the topic.
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