Clare
Sometimes it can take up to a week to implement...if you can't get him to take it within 5-10 minutes I would put him back down right away. If you find after about a week of trying, that it's just not working I would then concentrate on the clusterfeeding instead. The dreamfeed sometimes takes a few days to get established, I'd recommend that if its not working, you drop it for a week or 2, and then try it again.
HTH