documentclass{article}

usepackage{advdate}
usepackage{tcolorbox}
usepackage{pgffor}
usepackage{xparse}

NewDocumentCommand{journal}{+m+m}{%
begin{tcolorbox}[title={Date: #1},colbacktitle=yellow,coltitle=black]
Captain's log, stardate #1
tcblower
#2
end{tcolorbox}%
clearpage
}


begin{document}

% Doing ten (identical entries, apart from the date
foreach x in {0,...,9} {%
  AdvanceDate[x]
  journal{today}{%
    This day...
  }
}

end{document}