Theories for timing on picking up cornbread. Timing done without skipping cutscenes, meant for any% no escape. Cornbread allows you to skip picking up a gold leaf + visiting oil/potter vendors.

It takes about 6:38 from the time you stop speaking to the Farmboy in El Dorado to picking up artifact if you get cornbread, which is this route:

After talking to farmboy, you go back with the talisman, stick it in pool to drain and then put in the four parrot head codes. Go back and get the cornbread and then back across again to put in the regular code for the artifact doorway.

So, how long does it take from the ferry ride to the temple and then to the potter and then back to the temple again + talking with everyone you need to inbetween.

It takes about 8 minutes approximately just to get that done. So, in any% no escape, it makes sense to pick up the cornbread. You avoid having to do the extra ferry ride cutscene.

Overall, I do think the cornbread is faster for the speedrun, at least for the any % no escape and possibly for the any%, though I currently don't have the skills to test that.