A:
RONR does not attempt to specify what "ample" notice is, probably because it would vary from organization to organization.
One can imagine some places in the world where it would take two weeks to deliver the notice, in which case 13 days would be obviously insufficient.
Although I tend to believe 13 days is ample, it's up to your organization to specify it.
Since the bylaws are silent, and the assembly tacitly agreed with the chairman that 13 days were insufficient (when they could have raised a point of order), I have to say that - at least in this case, and setting a precedent - your organization has decided that 13 days are insufficient.
The best way to prevent this from happening again is to either amend your bylaws, or adopt a special rule of order, specifying the notice required.