I had the same exact question regarding when to apply so I sent and inquiry to the WorldBridge Service and this is what they sent back as a relpy:
Dear Sir or Madam,
Thank you for contacting WorldBridge Service, UK Border Agency’s commercial partner. We appreciate your patience regarding the response to your enquiry as WorldBridge strives to provide the most accurate responses to all enquiries. Below you will find the response to that enquiry.
At the end of March 2009, the existing student route will close and be replaced by the new student tier (tier 4) of the points-based system.
The start date of entry clearances may be post-dated by a maximum of 3 months. For example if you wish to travel on the 1st of December, do not submit your application until the 1st of September.
not provide immigration advice.
Depending on your nationality and the purpose/duration of your visit to the UK, you may need a visa.
To find out if you need a visa, go to the website
www.worldbridgeservice.com, select the country you are applying from, and click the “Visa Information” link at the top left of the page, or visit
www.ukvisas.gov.ukIt is the applicant’s decision as to which category of entry clearance he or she would like to apply for.
In order to obtain information about how to apply for a UK Visa, please access the website
www.worldbridgeservice.com choose the country from where you are applying and click on the link “How do I apply.”
Please note that visa fees can change at short notice. Kindly visit
www.visainfoservices.com on the day of application for current fees.
Please see the links below for further information regarding Students and Dependants:
INF 5 – Students
https://www.visainfoservices.com/admin/Documents/Global/Bundles/05A%20-%20Students%20and%20Dependants/INF%205%20-%20Students_12-14.pdfStudent SDC - VAF3
https://www.visainfoservices.com/admin/Documents/Global/Bundles/05A%20-%20Students%20and%20Dependants/Student%20SDC%20-%20VAF3.pdfVAF3_Guidance
https://www.visainfoservices.com/admin/Documents/Global/Bundles/05A%20-%20Students%20and%20Dependants/VAF3_Guidance-10Dec07.pdfINF 1 – General Information
https://www.visainfoservices.com/admin/Documents/Global/Bundles/01A%20-%20General%20Information/INF%201%20-%20General%20information_12-14.pdfVisa Application Submission Information
https://www.visainfoservices.com/admin/Documents/Region%20A/United%20States/Bundles/Visa%20Application%20Submission%20Information_United%20States.pdfVisa Application Fees for the United States
https://www.visainfoservices.com/admin/Documents/Region%20A/United%20States/Bundles/Visa%20Application%20Fees%20for%20United%20States.pdfPlease note that you will not be able to respond to this email. If you have additional questions submit a new enquiry via email free of charge by visiting the WorldBridge website at
www.worldbridgeservice.com. When submitting a new enquiry, please reference the case number from this particular email to ensure thorough processing. Note the case number can be found in the subject line of this email.
EX: Reply from WorldBridge Services for CaseNumber :00000123.
Thank you again for contacting WorldBridge.
Very sincerely yours,
WorldBridge Service
WorldBridge Service is happy to provide you with this information. Please note, however, that the decision to issue or refuse an entry clearance is made solely by Entry Clearance Officers at the British embassy. WorldBridge staff has no power or influence over the success of applications. WorldBridge staff may offer application information but may not offer immigration advice.