Date          Header1           Header2
01/01/2016  value_header1_1    value_header2_1
02/01/2016  value_header1_2    value_header2_2
03/01/2016  value_header1_3    value_header2_3
04/01/2016  value_header1_4    value_header2_4
05/01/2016  value_header1_5    value_header2_5

Date          Header1         Extra column
01/01/2016  value_header1_1   header1
02/01/2016  value_header1_2   header1
03/01/2016  value_header1_3   header1
04/01/2016  value_header1_4   header1
05/01/2016  value_header1_5   header1
01/01/2016  value_header2_1   header2
02/01/2016  value_header2_2   header2
03/01/2016  value_header2_3   header2
04/01/2016  value_header2_4   header2
05/01/2016  value_header2_5   header2

=transpose(split(join(";",'Daily data'!B1:B,'Daily data'!C1:C),";"))

={filter({A2:A, B2:B, iferror(A2:A/0, "header1")}, len(A2:A)); filter({A2:A, C2:C, iferror(A2:A/0, "header2")}, len(A2:A))}