How can I earn my guinea pigs' trust?

I've had my 3 pigs a week now. Although they are not as nervous as when they first came last weekend, they are still really nervous and stay in their bedding compartment most of the time. I've spent time with them over the week talking to them and stroking them (when they would let me), and they had started to come out of themselves a little. I had to clean their hutch today, which was obviously traumatic as they were picked up for the first time. That was a few hours ago, and now they are hiding back in their bed again and have hardly come out to eat. When I go to see them and talk to them, they cower in the corner and bury themselves in their hay. I feel now like I've undone everything we achieved last week when they were starting to show signs of trust. How do I get them to understand that I'm not going to hurt them and that I'm not a predator? I purposely haven't been handling them daily as most of the books/websites advise to introduce this slowly, and only when you've gained their trust. I know its going to take time, but on average how long does it take for a guinea pig to fully settle down and get used to his surroundings? I've obviously freaked them out by handling them today, so how do I start to get their trust back?