First of all congratulations!
Are you having a church ceremony or register office? I'm just wondering if it's register office that's only about half an hour what are your guests doing from 4.00pm to 05.00/5.30pm whilst you have your photos taken? Or is it quite a drive to your venue? If it's a church wedding then I guess the ceremony takes longer and it should work out alright.
What would worry me is that it's quite a while for your day guests until they get anything to eat. Assuming they will arrive about 3.00pm for your ceremony it's 4.5 hours until they get anything to eat. If you want to keep it this way I would make it clear on the invitation that there will only be evening food so they can have proper lunch at home. Or if your budget allows it serve some canapes with the drinks upon arrival at the venue.
Also I would swap the timings of the cake cutting and the buffet food. Half an hour seems a bit tight. People will walk about to get food, still eat or pop out for a cigarette after they have eaten. I think it might be a bit difficult to get everyone together for the cake cutting moment. Maybe do it right before the buffet food is served so you can still have it as dessert what I guess was the idea for your above timings.
I hope this helps. Good luck with planning everything!