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If your images have commercial value there's usually very little lag between uploading and selling.

That being said, you chose the worst month of the year to begin uploading your stuff - demand is generally lowest this time of year. I ceased uploading after the first week of December, then resumed so my images will 'go live' in the first week of January. It's also important to upload images when they are in demand (e.g. you're better off uploading a shot of colorful trees in late summer or early fall than in winter).

Like Sharply_Done, I stopped uploading a couple weeks ago and am resuming now. The last 2.5 weeks of December are a wipe-out.

It may be just my imagination but it seems like sales do take longer to get going at StockXpert. And last month they had a glitch which caused some new images to not show up in searches for weeks.  StockXpert has a thread on this in their forum (which you might look at if you have not seen it and fear that some of your images were buried as a result of the bug), and in the thread an admin says, "Of course you can delete your images and re-upload at any time."

So if you want to give your images a fresh start in January, you could delete an re-submit.

Keep at it. I was new a little less than a year ago, and things were slow. But the sales is regular with StockXpert . That's one thing they are good.
And yes, keep special notice on how quickly you sell. As sharply-done mentioned, there is very little lag between sales and upload.
I got a few sales that started almost the very next day or seems like it, and it's repeating . You learn from all these little things, and you shoot the style of those images that are repeating sales. 
More important is you don't stop to enjoy, sales or no sales. If that happens, give it up. BUT before you do, give it time. You will not be disappointed with StockXpert.