Ideal working hours are the hours during which you are the most productive. This can be at any time of the day. For some people this time is in the evening, for some the morning.
The challenge comes when balancing your own ideal working hours with those of the members of your team. If you are in a truly collaborative team, the most productive time is when everyone is in the office.
Some companies completely disregard ideal working hours and mandate that everyone be in the office between certain times. Others allow everyone to set their own working hours. The former sacrifices the individual for the team and the latter sacrifices the team for the sake of the individual.
Like everything else in life I believe there should be some balance between these two opposites.
An interesting discussion to have with your team is around each persons ideal and then setting core working hours based on that discussion. This should allow some flexibility for the individual and established team time too.
Again like everything else in life, you're not going to always be able to please everyone.
As a final point, sometimes an individual may have to sacrifice their own ideal working hours due to their personal situation. This us true in my case, when I work best in the evening but for my personal situation it's best that I start work early in the morning.
What are your ideal working hours?