You can make these in advance and store them, with the caps on, in the fridge, for up to 4 days before serving. Do not freeze.
You can get larger syringes, but I promise you, syringes get huge as they get to 1-ounce and larger.
You want to keep the jello thin enough so that when it sets up, it won’t be super hard to squirt the shot into your mouth. If you want them even thinner than the recipe, you can add a bit more vodka, but be careful, or they won’t set up at all.
Don’t rest the tip of the syringes on the bottom of the bowl to fill them. You don’t want to end up with leftover jello gunk in there.