1. Can regular saline solution be used to rinse contact lenses?

Regular saline solution, ie. a sterile NaCl 0.9% solution, fe. the one made by Braun. The booklet indicates that it can be used to wash eyes. It cannot be used for infusions or injections.

I think it's unbuffered (which as I understand means the pH isn't right) and that may be a downside. I wonder what real difference do the differences (if there are any) make, ie. what problems may occur?

Are all saline solutions made by contact lens producers buffered and contain boric acid and sodium borate?

This is for use with hydrogen peroxide solutions - to rinse the lens case and lenses itself before wear as directed in peroxide solutions' booklets.

2. For how long can one use a preservative free saline (for use with contacts) once opened? I get mixed feedback on this from https://www.purilens.com/purilens_faqs.html Should I really recommend using disposable 5ml vials or use in 15-days once opened? Is there any scientific or a respected "good practice" consensus on this? Perhaps optometrists in some countries get training for this?

Also, I notice that some saline solutions dedicated for contacts contain preservatives in amounts similar to those one can find in contact lens solutions, eg. Equate Saline contains 0.00003% DYMED + EDTA 0.025% while ReNu MPS 0.00005% DYMED. What's the point of using saline that contains preservatives?