How long are the LOR?????

Okay,

All of my letter writers are male.

First, dental clinic manager (that I work in) said that he would write me a reference letter, and after he wrote it, he gave it to me to read it. The letter was great, but the length was like 2 paragraphs total of like 12 lines. That looked sort of short!.

Second, my chem professor totally agreed to write me a letter but he is telling me that we would meet one afternoon and talk about my plans, goals, previous experiences etc and then write the letter right away and send it off the same day to our LOR file services. Is that possible!!!

My stats are not too great, and I'm worried that the length of these letter would not get me into a dental school.
In general, how long are the letters?
My high school english teacher wrote me a full two page recommendation for my high school scholarship, and compared to that, my dental school letter is way too short. What should I do!?