The engineer told me also not to turn off my equipment for the next 3 days, he even told me to leave it on 24/7...
BT FON seems to be off on the home hub by default.... I hope so.
I would go here www.bt.com/btfon and click on "Check the status of your BT FON account" and enter your details. From what I've read the router comes with FON disabled but it turns itself on after a few days. I just opted out the first day by going to the link I posted.
What exchange are you on? By the looks of things the amount of people connected to the exchange can make a big difference at peak times..
I don't know if it's as simple as that, my exchange serves 36,086 residential premises and 1,783 non-residential premises and I get the full 38meg 24/7. The only time I've had a slight slow down was when the Royal wedding was on.