Eviction letter, late rent

[Mae Tariman]

Hello peeps, my renter has not paid September rent yet(due Sept 25), October rent is due in 2 days, I sent them first notice regarding Sept rent being 28 days late. How soon should I give them eviction letter? Is there like a legal format for eviction letter? Hopefully they pay this week for 2 months rent... 

also, I mailed them addendum for lease agreement that rent should not be late more than 10 days, is this legal? thank y'all