I have been using this Diaper Cover Pattern, that have a nice tutorial, but I'm also making some adjustments to facilitate the work, in terms of difficulty and speed.
The pattern is easy to follow, and as the differences in size are not very big, I use the large one, even if my niece is only 10 months (she will grow and the diapers covers will last more).
The first one I did, I followed exactly the tutorial, but used some jersey fabric, and worked well. It was before I bought my serger machine, so it was made only with zig-zag, to accommodate for the jersey stretching.
But for the second pair, I used some fabric, not jersey, that was very rigid, and I was experiencing some difficulties in the legs casing.
So, I did my first adjustment - elastic thread for ruffling the legs (you have a tutorial here, if you need). This alteration is not a big "time saver", but it's much easier to do.
The second adjustment was to cut front and back in one part, without the seam between the legs (less 5 minutes spent in cutting and sewing).
But the important time saver adjustment was found this morning - using my serger machine for the finishing of the legs and waist, combined with the elastic thread. In a little bit more than 2 hours I made 8 pairs, most of them in jersey, but also including one in lace and another in fabric.
And I have more on the way...