Accept use in sqlplus
It looks like your ACCEPT prompt includes quotation marks. But quotation marks are also used to delimit the prompt string, so if you want to include those characters into the prompt, you need to double them:

… prompt 'Fecha de inicio (''DD/MM/YYYY-HH24:MI:SS''): '
… prompt 'Fecha de fin    (''DD/MM/YYYY-HH24:MI:SS''):'


Although I think you could simply omit them, since this is just a prompt:

… prompt 'Fecha de inicio (DD/MM/YYYY-HH24:MI:SS): '
… prompt 'Fecha de fin    (DD/MM/YYYY-HH24:MI:SS): '