@Jacob PaulI believe your flowfiles having source-date1 attribute with value 20181119112100.
Then change your update attribute property values as
source-date as
${source-date1:substring(0,8)}
source-time as
${source-date1:substring(8,13)}
Then update attribute adds these flowfile attributes for all outgoing flowfiles from UpdateAttribute processor.
In addition you can also perform same kind of operation without extracting as attributes using QueryRecord processor.
Configure/Enable Record Reader/Writer controller services and use apache-calcite's Substring function to create source-date,source-time columns in the flowfile.