There are several red flags in your post that point to a company in severe financial distress. These types of companies are desperate and many times the owners think if they can just make it for 3-6 months things will turn around. Unfortunately the measures they take to get them through are likely to doom the company in the end. When the company goes bankrupt there is no money left to settle unpaid payroll, or legal judgements.
he changed the notice period from 1 month to 3 months and the salary
will be held for the total notice period.
This is done to give the owner an excuse not to pay someone for their final notice period. It saves the company payroll. The only way that an employee is likely to get their final check is after a lengthy legal battle that will likely draw out over a year.
if you late 15 minutes your half day salary will be cut
Here the intent is to save money on payroll. Right now it is 15 minutes, before long it becomes 5 minutes then suddenly despite being here 10 minutes early he said you were late getting in. It is nothing against you personally. The stress of losing your business and everything you have sunk into it can drive people to do seemingly insane and cruel things.
and the AC will only be switched on for 2 hours to save on the
This will only save a tiny amount of money, if any, but it is a sign of how desperate he is. The owner likely knows that it will be very hard to pay the electric bill in the coming months. So he is trying to keep it low hoping the company will leave him on longer. (They won't)
This is the part that I hate. You need to protect yourself. You are unlikely to receive many more paychecks. The excuses will come about how the package they were to be delivered in was lost, They have been mailed to your home, the payroll company forgot to process it and now will not be able to until the Xth. They are all excuses that I have heard while working for start ups. None of those companies lasted for 2 months after they missed their first check.
If my read of the situation is right your career is unlikely to be impacted. Companies go out of business all the time and others understand that. Going to work at a new company as soon as you can is the best bet. I would not worry about any notice, as the same reason he does not worry about being sued is going to protect you. The company is not going to be around to file a suit against you.