The UKBA states:-
"You can apply for your visa within three months of your intended date of travel. We are only able to post-date visas by a maximum of three months from the date of the decision on your visa application. You can enter the UK anytime after your visa issue date but not before."
Normally the visa will be valid for 27 months from the start date, so plenty of time to complete the required 24 months living in UK before ILR application.
Hope that helps