From what I have been reading, it seems the norm now is to have a 15 minute viewing as part of an open day and then final bids to be submitted.
My previous experience of house buying has been to have a first viewing or probably 15-30 minutes, think about it for a while and if interested go back for a second viewing, maybe with a tape measure and more questions, maybe with someone else to get their opinion.
I find it hard to get my head around making such a big decision based on 1 quick viewing.