Confusion on Late AF

Shevon • 25 year old LPN in the state of Florida. Engaged 08/06/2015. TTC #4. Irregular menstruals, tested negative for PCOS
What is glows definition of a late period. I keep putting late period and it pushes it back two days. I have not started my menstrual as of yet and im not sure if thats what I shoulf be doing or just marking X. I need a little help understanding how to record things in this application.