When making an amateur knot must one have in mind to undo it within 24 hours?
If the knot is a type of knot which is at times opened within 24 hours, and certainly if it is meant to constantly be opened, then there is no need for one to intend upon tying it on Shabbos, to open it within 24 hours. Furthermore he is not even obligated to open it within 24 hours. Nevertheless, it is forbidden to specifically have in mind to undo it after 24 hours. Thus it is only remains permitted to make the knot in such a case if one has no intent on when he will untie it.
If however the knot is never commonly opened within 24 hours, then it is forbidden to be casually tied [unless one has intention to untie it within the same day].
May one untie an amateur knot which was made without any specific intent regarding when to be untied?
If it is a type of knot that one at times unties within 24 hours, and certainly if it is meant to constantly be opened, then he may untie it even if when it was made it was made without any intention of when to untie. This applies even if many days past since the knot was made.
However if made with intention to untie past 24 hours, or it is a knot that is never untied within 24 hours, then it is prohibited to untie.