Primer still a little tacky, any advice?

I sprayed the first coat of Testor Enamel Gray Primer (from a spray can) two nights ago and the model still feels just a little bit tacky. Does this mean it's not quite dry yet? How long does it typically take for primer to dry? If it should have dried by now does that mean I put it on to thick?
I'm thinking the best thing to do is to let it be for a few more days and then try to sand and polish it a little bit before moving on. Is this the best approach?
One last thing, how many coats of primer should I use before moving on to the final color?

Well, you might get 10 different answers here but imho, one coat is enough as long as you got a good smooth cover and it didn't reveal any body flaws that need repair and spot repriming. You're just laying down a surface for the body paint, no need for any depth to it unless you're trying to cover something up (which won't work anyway...), too much might start texturing and spoiling the body details. My guess is it's sticky because you laid it down a bit thick. But that'll turn out ok - it's smooth right? - just let it dry thoroughly. If it is smooth, no need to sand it I think. Maybe some very fine wet-and-dry under the tap if you're going for a flawless smooth finish. As you can see it all depends on your preparation, a first class prep job makes your painting much easier. Good luck with it...

Enamel primer can sometimes take a long time to dry, especially in colder conditions and often does remain 'tacky' for a lengthy period.If you want a quicker drying primer then I suggest the Tamiya Surface primer available in aerosol form.It lays on very smoothly and dries quickly being a lacquer based paint.But with the enamel I would just leave it to dry for some more time and keep checking it, you will know when it is ready because it should be hard and less 'tacky' to the touch.I have sometimes found with enamel based paints that adding just a few drops of cellulose thinner into the mix when spraying that it helps to lose that 'tackiness' Use your enamel thinners as usual but just add a few drops of the cellulose as well and it will hopefully help.I used to use this all the time when I built aircraft models and it worked very nicely.

The problem with Testors gray enamel primer is the fact it's enamel. It takes a long time to dry and it's not sandable. It covers bodywork decently, but it's more of a satin gray base coat vs. a real primer.

Tamiya primer is infinitely better. It dries much faster, it's not nearly as thick. It likely doesn't cover quite as well, but it's a real primer and it goes down very smooth.