You will be able to book your appointment date for 28 days before your visa expires or 28 days before the day of arrival if a spousal visa. You must apply before your visa expires. You will need to check the appointment booking system earlier for available dates as they have booked in the region of two months in advance. See Border Agency information below: Apply to remain in the UK with Family Apply to settle in the UK - ILR Extending your Tier 2 Work Visa

Don't book your flight until after you get your visa approved and you check it for errors, just in case your visa is refused or delayed. You could lose the money you've paid for flights. You can include a sample itinerary with your application, such as the flight search results selected as a potential itinerary. "Travel documents" as referred to in the biometrics letter means your passport .

There is a UK visa processing time table at https://visa-processingtimes.homeoffice.gov.uk/y/united-states/all "Processing times vary depending on a range of factors." As of Feb 2015: Visit Visas Most UK visit visas are processed within 10 days, but some can take up to 60-90 days. Most Business visit visas are processed within 10 days but can take up to 30 days. Most Family Visit Visas are processed within 10 days but can take up to 30 days. Most transit visas are processed within 10 days. PBS...

No. You have to show that you were in the UK for exactly three years prior to the date that you apply. You cannot apply before you have been in the UK for at least 3 years. The application date is believed to be the day after you mail it, so if you send it on the first of the month, the application date is the 2nd. It can take a few months to process and it is advised not to travel during this time. After processing it can take a few weeks to have your citizenship ceremony. You must also have a...