stop worry you've done the right thing
you've applied as early as you could, you could have left it upto a couple of days b4 your visa expired.(the lastest you could apply)
but its always best to apply asap, so if there are any problems with your app you have time to sort them out
24 or 27 months the earilest you can apply for ILR is upto 28 days b4 you've been in the uk 2yrs.. so no problems
