I'm using origami to digitaly sign a pdf.
Is it possible to use OpenSSL::PKCS7.sign to sign a pdf and pass as a parameter or as an attribute an specific date to be the date of signing?
If not is there any way of accomplishing this?
I have been searching but found nothing on it.
What you want makes no sense from security point of view. You are actually asking "how do I spoof signing time in my documents". Well, you can't do this without capturing control over one of authorized TSA (timestamping authorities) in one way or another.
Update: In general it's possible to put any time to PDF signature as one of its attributes. As I look into Origami's source code, I don't see any way to put time to the signature.