Listing absences before the basing period

Dear,

I first entered the UK in 2011 to study. I started working with Tier 2 visa in Sep 2016 and doing an application now based on the 5-year working route. I would like to ask for advice to respond to 2 questions in the form:

1. When did you first enter the UK?
Should it be 2011 or Sep 2016? I assume it should be Sep 2016 as it's the period I base to apply the ILR.

2. I need to provide a list of absences from the UK
-> Should I list all the days since 2011 or just the ones after Sep 2016?

Many thanks,

Phong

1. It does not matter what date you put
2. Only the last 5 years under Tier 2

Many thanks Zimba for your swift reply.