booking of appointment using new online system

Hi!

I'm new and am grateful for any advice anyone has. Thank you!

I received my Stage 1 and am trying to make arrangements for Stage 2 of Tier 1 Exceptional talent visa. As I'm transferring from a spouse visa I need to fly home and can't apply from within UK.

Question: How far in advance can I book my appointment online? Is it 1 month? I intend to return in June but cannot book that. So I can't book my flights etc.

Also, I want to book the priority service (5 days) - but that doesn't show up on the online form system (which I have successfully submitted, but am stuck and cannot proceed beyond the 'ale an appointment' bit). Instead it only shows 'standard', 'premium' and something else about out of hours appointment. Do I chose 'standard' and go on the separate vfsglobal site to book priority? 'Premium' apparently is not the same as 'premium' in the UK as in same-day processing, it means you have access to some comfortable lounge seating which I don't need.... So basically I

Thank you!

Best
V