Access 4pm or later is not unreasonable: access is not being denied or being limited to an unreasonably short time (e.g. 30 minutes) and can apparently be on any day--i.e. there appears to be plenty of opportunity for your inspector to get in. Since there are also plausible reasons why access might be limited (the realtor wants to be there, and is only available after 4, for example), with the breadth of access you still have (any day; late afternoon on), this would not be considered unreasonable or a breach of any of the seller's obligations.