RESIDENTIAL TENANCIES ACT 1987 - SECT 46
Section 46 of the Residential Tenancies Act:
(1) It is a term of every agreement that the owner may enter the premises in the following circumstances but not otherwise —
(1)(g) for the purpose of showing the premises to prospective purchasers, at any reasonable hour and on a reasonable number of occasions, after giving the tenant reasonable notice;
Therefore no minimum notice required, as long as the notice is 'reasonable'. As a property manager I showed people through the house, never had an issue with people looking through others items. Generally people were pretty respectful of this and glanced through bedrooms etc more to get an idea on size/layout.
Can definitely stay there if you wish. It just makes it awkward for prospective buyers as they feel like they are invading on you. It's not common but you have every right to do so
