I am applying for tier 2 pbs dependant visa extension. I have submitted the online form and paid for premium service, but the earliest I could book is the 4th of September... I want to apply earlier as I will have to travel on the 7th

- do you please have any tips to get an earlier slot?
- is it ok if i apply when i get back on the 23rd of september, knowing that my current visa expires on the 15th of october?
Many thanks in advance for your help!