It depends on when you submit them. I usually go through them at least every Tuesday and Thursday. (more often when I have time...... we're a lot busier than you can possibly imagine. Really!)
If you submitted your picture more than a couple of days ago and it's still not showing up, then there might have been a problem with it. I do get a lot of little red 'x' submissions. I can't do anything with those but delete them.
Earlier today, I activated all the pics that were submitted in the past few days.
So, you may want to try submitting your picture again. (but I won't be able to activate any of them until Tuesday the 8th... I'm going wild boar hunting!)