When to ask for LOR from a new professor?

[ToomuchLes]

As a transfer student, its quite hard to form relationship with many professors in a single academic year. Currently, I have 2 LOR that will fully explain my background, research, and writing abilities, as well as my strive to pursue graduate studies. Nonetheless, I still need one more LOR.

 

Here is my dilemma : Im taking two seminar classes, that meet once a week for 4 hrs to discuss our weekly readings, and writings. From what I've noticed, Im starting to gain favor with both professors, however since class started in late Sept, I've only interacted with them 4-5 times. I would very like to ask both of them to write me a LOR however Im unsure when I should ask. My first application is due Dec 5th, and my last on the 16th. When would be a good time to approach them for a LOR? 

 

I was thinking the week of Nov 11th. On that same week, I shall also turn in my completed research paper which is due end of the quarter in mid Dec. 

 

Comments?