1) Skilled visa - upto 3 months in advance, is it 3 months or 90 calendar days? 2) Waiting times inside UK with priority. Both elaborated on below.

Just want to understand the UKVI rule which says, you can apply 3 months in advance?

1. So if lets say, my job starts on 1 Ocober, can I apply for skilled visa on 1 July (3 months), or do I need to wait till 3 July (90 days)?

2. What are the recent decision times from application to decision for priority (not super priority) for applying within the UK in your experience? I want to book some travel, but I know I cannot leave the country while my decision is pending.

Thank you!