I am not sure if using Borax one will find it to be a bug repellant or not?? I just refuse to trust something as important as eliminating all bugs in whatever state they be. I use No Pest strips, cut to one inch wide strips, wrap loosely in saran wrap so they do not come in direct contact with either my hands or the hackle. Do not know if they would cause any problems but again, why take the chance. Many experts tell why you should not use them?? Whatever toots your train. Everyone is authorized a personal opinion. I trust NPS and I really do have many more pieces of hackle than any tier to protect. ( I trust only one other method and that is using the method I have gone to school and have been authorized to do by the UDSA for shipment into Australia. Very expensive and dangerous for one not totally familiar and one must have the proper equipment. So I will not even go into that one.) Keep it simple and have fun, go fishin and or tie flies.
10 - 14 days is fine. Like I said, depends on the temp where you hang / dry them. Caution: Too long on the cardboard might make them very difficult to remove. Do not hang in direct sunlight. Sunlight can and does damage hackle. Yes, if you see hackle displayed in a shop and see direct sunlight hitting it. Be careful. Just laying on your tying bench where direct sunlight will hit it is BAD! Put it away after tying.