The whole "imprinting" with ducklings is more of "window"....and after having hatched many a duckling in an incubator that saw me first for several hours while I interacted with it and cared for it, went in a brooder in the garage overnight so I could sleep without all that darn peeping, then acted utterly terrified of me when I brought the brooder back in the house the next day I began to research the whole issue of how ducklings imprint, Turns out they imprint in roughly the first three days-ish. Supposedly the imprinting drive is strongest when the duckling is between 12hrs to 48hrs of age, but I don't know that that follows through as it seems like being around them a decent amount for the first week still works as good. Another thing to note is that these ducklings don't imprint on one thing only. They tend to imprint on each other, their "mom" figure, AND their brooder all together. So if any one of these components they are used to are missing they will freak out more or less depending upon their individual personalities.
What I am saying is that these ducklings will be just fine seeing you and each other first. Then you make sure they are dry and fluffed up and have had their beaks dipped in their water source and they know where food is. Once that is complete, stick them with mom and I highly doubt the mom duck will notice as ducks I have had really aren't the brightest crayons in the box usually. The babies won't be totally imprinted on you and they will probably just be buddies with you, mom, and the other siblings. If mom still rejects them anyways, then you are stuck brooding them yourself.
Since you don't have an incubator for them to hatch and fluff out in you can use some light bulbs instead. We had situations where we had straggler babies hatching that were squacking up a storm so loud we couldn't find anywhere to put the bator in the house where we wouldn't hear them even with box fans on for white noise. In our experience these way behind "stragglers" never were able to hatch on their own, and when we would help them hatch we typically seriously regretted doing so as the birds nearly ALWAYS had some sort of deformity and/or major issue with eating and/or a major temperament issue and we had to cull them anyways. So since we didn't have much faith in the screaming stragglers hatching we put them in the brooder under the light at 95 to 100 degrees, with a bowl of wet paper towels near where they were to bump up the humidity so they wouldn't shrink wrap and we used thermometer/hygrometer to measure these values in the brooder. They hatched just fine over night and fluffed out successfully in the brooder instead of in the incubator.
If you do not have a brooder light, then you can improvise overnight till the stores open with an incandescent bulb that is 45 to 75 watts (depending on what yah have laying around). The key thing is that the lower the wattage of the bulb and the colder the room temp is the closer the bulb will need to be to the eggs to make them 95 to 100 degrees. Put them in some form of a brooder which for hatching could be a plastic tub, a cardboard box, heck...even a shoebox. I have also used heating pads before in emergencies to keep babies warm in the absence of a brooder light/mom. Just be careful you don't start a fire with the light bulb or heating pad and that the temp is about 95-100 degrees, the babies have some blankies to snuggle under/into as they dry off, and there aren't any bad drafts esp while they are wet and still fluffing out.
*****Oh, and often mamma does leave the last couple stragglers behind if they are too far off from when the majority of the babies hatched as she instinctively knows that often the ones that don't hatch in time may never hatch on their own as they are deformed or have some other issue not compatible with thriving and surviving...so don't be surprised if there is something wrong with the ones left in their eggs even if they peep as though they are healthy and well...
If the babies end up "shrink wrapped" due to lower than ideal hatching humidity since you need to make an impromptu brooder/bator for hatching check out the complete info on this site that is AWESOME a gal did about "how to assist with hatching"...it will tell you in detail everything to do. Try to keep the humidity up as much as you can in your impromptu brooder/bator, adding the plastic bowls with soaking paper towels under light near the eggs helps as does covering the eggs with a layer of paper towels/cloths, and dabbing some damp, warm water on the membranes if exposed or lightly spritzing the egg since this is a duckling especially (they need higher humidity at hatch than baby chickens and quail I have noticed).
Hope this helps and let us know how it goes!!
