This surcharge came in on the 6th April 2015, we will be applying for FLR in a few weeks. We pay from the 6th April or from when we apply for the new visa?

If we apply from the exact date being 30 months living in the UK and pay two and a half years "£500" then this is cutting it close to the visa and the surcharge running out before getting the ILR.

I know this is not the best idea but would it not just be easier to pay for 3 years a few weeks before we apply for FLR and that will cover it easily at both ends of the visa if we do not have to pay from the 6th April?