OK, here's my way of looking at the problem.
You obviously need something to change during the 6 hour period. This could be one of two things:
Firstly, the content of your photographs could remain largely unchanged but the lighting could change. For instance your photographs could show the same landscape over a six hour period which goes from full sunshine, via a spectacular sunset, to a moonlit scene.
Or, secondly, the content of the photographs could evolve throughout the 6 hour period. e.g. you might show pictures of a quiet road, in the early hours of the morning, with only the milkman at work. Then you could show the gradual build-up of cars and people in a hurry during the rush hour, moving to pictures of unhurried pensioners chatting over their gates later in the morning.
Your post ("taking photograph every half an hour") is unclear about whether you're only allowed to take a singlephotograph every hour, or a series of shots. If you're restricted to a single photograph it might be better to reflect changes in the light. If you're permitted to take extra shots it might be more interesting to populate your photographs with people.
Chris