Section 65 of the Licensing (Scotland) Act 2005 only specifies the times when 'off-sales' are prohibited. (i.e. not before 10am or after 10pm). There is no restriction upon the display of alcohol during prohibited periods.
I can find nothing elsewhere in the legislation which indicates that physical access to alcoholic products must be blocked during 'prohibited' periods. It seems to be simply up to each retailer to determine how they'll ensure that the law is enforced (while, at the same time of course, seeking to prevent thefts).
I would expect that all supermarkets would configure their EPOS systems so that they wouldn't permit the sale of alcohol during prohibited periods, and to display notices advising their customers of the law. Some supermarkets might find it convenient to physically block access to booze (in order to avoid possible confrontations at the check-outs) but there seems to be no obligation upon them to do so.
Chris