Not used time columns in SSRS so this may not work, but will need to create an expression in the tablix something like
Fields!Shift_Start.Value + " - " + Fields!Shift_End.Value
You may need to convert the values to strings first.
Or do it at the DB layer and convert the times to varchar and use string concatenation something like
convert(varchar(5),shift_start)+ ' - ' + convert(varchar(5),shift_end)