I agree with VLAZ, that this question needs to be seen by somebody who can comment on biology. However it clearly has a social and psychological element too.
The first thing that comes to mind for me is that a 2-hour longer day may lead to people becoming irritable and/or depressed as the day is not yet done (ie., it's not time to turn in for bed yet) and there are still two hours to go. It may introduce a social expectation to stay busy for those extra 2 hours which some people may not be prepared for and may not want. While that may lead to people becoming over-tired, it may also engineer resentment towards whoever is imposing the pressure to be productive for those extra two hours.
I'm thinking about mild sleep deprivation on a daily basis that would be mitigated by plenty of sleep. However, I do know that sleep deprivation affects people quickly, and if most of the population feels this way then chances are, there is going to be an increase in the net number of arguments happening between people, people damaging relationships by being tetchy at each other when they don't mean to be, and so on. I think somebody who understands sleep cycles better than me could comment more on this.
People who need fewer hours of sleep per night may also find themselves falling out of sync than those who are happy to stay in bed for as many hours as you give them.
Advice from somebody with neurology training may also help as I suspect that the humans would adjust to the longer day so that the above no longer affected them. Whether the adjustment would come in the form of neuroplasticity - the ability to adjust to a different length of day - or evolution over many generations is another question.