Talk to your fabricator and ask him if he can make you the piece out of the same stone, and tell him that while you know you have to wait on the vanity, you'd like the threshold right away. The worst he could do is say no. Also, you might want to double check on the width. I have a feeling it might be just a hair OVER 5", like around 5 1/4 or 5 1/2". Most times, what I'll do is use a 6" threshold, and that'll give just enough overhang into the shower to provide for a drip edge.

Thanks so much everyone! In addition to honing, I'm also having the 12" x 12" tiles cut to 2x6 so let's hope the fabricator (who hopefully will also hone?) is affordable! The tiles I got seem somewhere in the middle, intensity or color-wise. The background is white and the veins are both grey and beige. Lots of plain white areas as well. I'm hoping in the end to have soft, subtle veining. One other quesiton: once cut, is there a direction I should do things to keep things from looking too busy? With slab, thicker and splotchier veins are okay but with tile, they go in all kinds of directions I imagine, without some sort of effort to make it all flow? Or maybe not - I have no idea! Suggestions? Thanks again!

One giant sheet of marble as a look is only possible with natural stone that is sequentially cut. Porcelain, even good faux marble, will always have pattern repeats. Therefore it's best to try to not pick patterns that will accent that fact. Turning them all randomly, and checking to be sure that you don't have repeats too close will give you a look that isn't so obviously faux.

Thinset at that thickness for your application with a breathable stone install cures in less than 30 days with a thinbed shower pan like you have . It should have initially been given a full cure prior to introducing water(after grouting). There is also rapid set thinsets that cure faster and theres also the wrong type of adhesive such as mastic or PRE mixed bucket grade glues. we dont know what you have. Dont be fooled by misinformation from some novice sales people on here about 2 months. If you want to verify if you have a grading/pooling issue as the cause. you stop using the shower. For at least a handful of days and perhaps put a dehumidifier in the shower to fully dry it out. it will either dry out and clear up or not. only time will tell. Since you have a thinbed pan you arent hurting anything(unless theres a pan leak not verified ) and best get used to it. The only other issue could be poor application of the wrong type sealer in that particular spot also not hurting anything. You chose a fickle material for a shower floor. and now reap the rewards. and you never clarified the flood testing process which is the only way to catch and correct a poor shower pan install before leaving a client with a wet mess like you may have...