Paul Carley, our phonetic listening post, has spotted an interesting weakform. On BBC Radio 4 of April 24 one of the presenters of the news and current affairs programme Today said: "And the time now is half past six". The preposition 'past' is pronounced with a schwa (sheva). Listen:
The speaker is Nick Robinson, a member of the team of regular Today presenters. I guess the weakform tends to be used only in such fairly tight-knit phrases as "x past y".