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.