Here's a chunk from the page at my site on glues for polymer clay:
. . . APPLICATION
The tube of E-6000 is very clear about the method that must be used for a creating a successful bond with this type of glue:
(...sand surfaces if necessary to remove lumps from surfaces before adding glue)
.......put E6000 on both parts that are to be attached
.......then let sit for a few minutes (tube says 10 min, but I find 3-4 min works best for me)
.......then press together
....also, enough glue must be used to avoid a "starved bond" (their term) ... but also a thicker glue area can fail more easily than a thin one
...for the clay item, I sand the area where the finding will be, then also wipe it with alcohol before gluing. Jenny.
....adheres in 5-10 min. (open time)... then hardens to a full cure in 24 hrs
... E-6000 also dries like rubber, so its seal also acts like a shock absorber if a piece is dropped (compared to superglue, e.g.).
There seems to be some variability in the holding power of E-6000 glue, as reported over the years:
...First, it must be applied correctly to work well (see just above in Application
.......I am still wearing 10-year-old polymer clay barrettes I made using E6000 ...people with glue failures may simply have not cleaned the pieces to be glued and/or they did not follow the instructions on the tube. Irene
...E6000 can withstand a lot of heat for short periods, but it can be heat sensitve after curing if exposed to sufficient heat or sun for a continuous
period of time . . .
So my guess is that most people don't use it as recommended (and haven't read the label), and since it will hold well under many circumstances never have a failure. But IMO applying it correctly would always be the most prudent thing to do whenever possible.
If you're gluing something small or lightweight though, and will never expose the glue to continuous heat or hot weather, you probably would never have a problem just pressing the two pieces together right away.