Yes, it's harmful. Humans are diurnal beings, so living at night and sleeping during the day places us out of touch with the laws of nature.
Not to mention, the Sun symbolises activity and vitality. This is why the majority of plants and animals are more active during the day as well. The Night is naturally a time for relaxation, spiritual and awareness. That's why the night is dark and it's not light. That's also why humans can only see during the day and not at night.
The only way a human being can see at light is by lighting a candle or using other artificial lighting. Artificial lighting is one of the main causes that nowadays brings people out of balance with nature and creates clinical impairments such as people thinking they're "night owls" which is not really a thing.
Now, don't get me wrong. There is nothing wrong with artificial lighting per se. It's just about the way the enemy made it popular. What is used by most people nowadays is lighting that use the full spectrum of light, which is not supposed to happen at night. You're supposed to see only a limited part of the spectrum, which is why candles are still okay. The only way to contrast the unnatural lighting is to use blue-light filters. True ones, not the fake "night light" provided by Windows 10 and Android devices.
Unnatural lighting tricks your pineal gland into behaving like it's still day when it's not. This over time impairs it, and it will no longer produce melatonin in sync with the natural rhythms of human life. This affliction, combined with the poor nightlife habits most people have nowadays (i.e. late night gaming, late night watching tv, clubbing, going out for a drink, staying up past midnight etc) over time affects a large percentage of the population into believing they are nocturnal beings. However, that couldn't be further from the truth, and nature proves it as I explained it before.
What's natural and you'll see in people with abundant health and no ridiculous work demands is to wake up when the Sun rises and start winding down when the Sun sets, until you go to sleep at a decent night time, which is naturally between 8 and 11pm depending on the individual's natural inclinations. There's a small minority who also naturally wakes up before dawn, and a small minority who needs 1 or 2 hours after.
When I mentioned nightlife, this is not to say that our ancestors, who were much more in tune with nature, did not enjoy themselves at night ever. This was done once in a while on specific occasions such as Pagan festivals. Not every weekend, and definitely not every night forever like many young people nowadays do, nor for months like you admitted doing.
Most people also make the mistake of eating too close to bed times, sometimes because of inappropriate (I would say criminal) work conditions, other times because of unnatural habits developed over the last few decades after WW1. You need to give your body at 3 hours to finish certain phases of food assimilation, and got to bed after your stomach is empty, in line with natural law. Eating to close to natural bed time not only hinders digestion but is also an obstacle to your sleep quality and certain processes that your body naturally performs at fixed hours during the night.
In conclusion, human beings should avoid being awake at night and sleeping during the day just because of deleterious whims such as negative habits or a negative social life. If someone is in a position where they have real responsibilities during the night such as work, they should work to relieve those responsibilities and achieve a better balance. If someone has a child, it obviously cannot be helped until they reach a certain age, but that is a temporary and necessary phase during someone's life, not what should become a lifestyle choice.
There are different methods to heal from this mental affliction, and they can easily be found online. Look into them and you will improve yourself. Be stubborn like most Zoomers and Millennials, and the consequences will be your health and your pineal gland. Other chakras will also be negatively affected by way of your health deteriorating.
M. Between 7-10PM most of the time.
