When is rent delinquent?

[Ryan D.]

Hi Bigger Pockets,

I am a young landlord that just has two rental.  One is going great and the other I just filled with a tenant that is causing me a lot of stress and problems.  

Over the weekend he said he will not pay rent due to some issues he has with the back deck. I had a contractor out a few days ago and it is up to code and safe.  

My lease with him started on the 15th of the month (he paid 1 month of rent then), so normally that's when rent would be due for the next month.  However, the lease he signed states the following (it wasn't updated from the previous time I used the lease when it started on the first):

3. RENT. Tenant shall pay to Landlord the sum of $1950.00 per month as Rent for the Term of the Agreement. Due date for Rent payment shall be the 1st day of each calendar month and shall be considered advance payment for that month. Weekends and holidays do not delay or excuse Tenant’s obligation to timely pay rent.

Here is my question:

It's not ideal that the lease started on the 15th, but states that rent is due on the 1st of the month.  

Should he pay 15 days in advance of the next month? Or 15 days into the next month?

I am asking because he is threatening to not pay and I need to understand when rent is considered delinquent to issue the "pay or vacate" notice.

Please help! 

Thank you!

Ryan