My rule of thumb now is I will pay no later then the time for the CCC to process they payment and to show up on your account. I use 3 business days before the due date as the latest I will pay the bill.
For me, late is when your payment is recorded post 12:00 A.M. the day after your due date.
If you prefer to tempt fate and increase risk of a "late" then you should listen to all the other definitions.
For me, I PIF each revolving account 10-15 days prior to the closing date. This way I optimize my FICO opportunies and avoid any problems with some CCC's that hold your payments for 15 days after they receive them.
FICO scores on November 17, 2014 (prior to applying for and being approved my mortgage)
EX=738 EQ=735 TU=754
FICO scores on March 4, 2015 after being approved for mortgage and buying the home, the mortgage isn't yet reporting. EX- 689 EQ- 739 TU- 739