
Play it by ear, they are still giving a large proportion of the pups nutrition, even if the feeds seem quick.
check your bitches body condition. with my girls (medium size breed with around 6 pup average)they are generally on around 4 times their normal rations or sometimes more.
By five weeks if they seem rather stout I may drop it to 3 times and see what difference it makes.
By 6 weeks it's usually twice normal rations and once pups are gone, if they aren't actually overweight I continue with 1 1/2 times normal rations as they will need more food not to loose condition when they drop their coats, and of course to repair their bodies.
With my first litter I cut my bitch to normal rations by 10 weeks and found she lost condition during the heavy post partum moult and took longer to get back into good body and coat condition.