Short Term Disability Paperwork

Christina
Has anyone else had to fill out their Short Term Disability and FMLA paperwork recently? 
For my job, I'll get 6 weeks full pay for Short Term Disability and 12 weeks (starting at the same time as STD) for FMLA - with the second 6 weeks unpaid or PTO. 
I'm having trouble answering some of the questions and was wondering if anyone had some ideas. They're asking for the date of "injury/illness" when I'll start to take the leave and the first day I'll be out of work. Do I just put an estimate for this, or list the month rather than a specific day? I don't want to lock myself into a date in case I go early or late. 
Any ideas are appreciated!!!