Timing

[HSMP holder]

Does anyone know what when I apply for Indenfinite leave to remain under HSMP, when is the start date for the five year period? Is it the start date of my EC, or the date when I actually arrive to the UK?

I have my EC valid from 1Apr 2007. But due to my current employment, I may not be able to go to UK until mid-April or early May. Does that deduct my resident period when I apply for ILR? In other words, unless I go there at the start date of my EC, I can never satsify that 5 year period, am I right?

Thanks for any advice.