ILR appointment Existing Vs new system

[SidG]

Hi,
28 days prior to my 5 years anniversary in UK is happening on 17Dec - i believe this is the earliest i can submit my settlement application(Tier 2 General) & pay. I've already filled the application online & have following questions:
1. Under existing system one can book premium same day appointment 45 days prior when one is getting eligible to apply- me & my immigration consultant is trying from last4 days(since Nov4) but unable to get a slot for Croydon (or any other center for that matter)? Everytime it says no appointment avaibale within next 45 days. As per my consultant till 2Nov everything was working fine but after that premium slots are NOT showing up. Have anybody booked priority same day appointment under existing system after 4-Nov -means same day appointment service on/after 17Dec?
2. New system: As i'm getting eligible of 17Dec to submit application & pay premium fees (£3018.20), than within 5 working days from 17Dec i can book next day decision appointment at any of the London centers- is this interpretation correct? Or i can submit application & pay 5 working days before 17Dec i.e. 10th Dec & then select 17Dec (which is 5th working day) for appointment? Which of the above is correct.
3. What if i pay today & submit my application & book 5 days appointment under new system- am i eligible to do so as as 28days prior to 5years anniversasy happening only on 17Dec?
Thanks in advance as new system is little confusing for people like me..
Sid