Many small companies do not have written personnel policies or a person trained to address personnel issues. Start-ups and family run companies often don't have the resources or knowledge to afford these and there is no law which requires them to do so. As companies grow, it becomes more important but some of these businesses are slow to catch on. It is very dangerous for them because they do not know the myriad of laws that affect them and it is not until someone files a claim or lawsuit that they realize the seriousness of their mistake or poor judgment.
Your employer's explanation that they can deduct the hours you missed because you are on probation, is a perfect example of this. They are wrong. If you are truly a salaried employee, they cannot deduct the hours for when you left early for a doctor's appointment. It leads me to suspect there may be other violations of your rights, as well.
I suggest you invest in a consultation with an experienced employment law attorney who would be able to examine the entire nature of your employment relationship for an opinion as to what this employer is doing right and wrong and to advise you on what options you have to address these issues.
They say you get what you pay for, and this response is free, so take it for what it is worth. This is my opinion based on very limited information. My opinion should not be taken as legal advice. For true advice, we would require a confidential consultation where I would ask you questions and get your complete story. This is a public forum, so remember, nothing here is confidential. Nor am I your attorney. I do not know who you are and you have not hired me to provide any legal service. To do so would require us to meet and sign written retainer agreement. My responses are intended for general information only.