Risky!
you should apply for a new TN now. Form now on, the TN will be granted for 2 years instead of 1 year. As long as you get your new TN, you can file your 140. The key problem is not when to file 140, but it is that you have to file your 485 and get your EAD before your new TN is expired. As long as you file your 485, you can apply for new TN again.