In my experience, it will stick even if you wait an hour or more. If think its dried to much, you can reactivate it with another coat of glue. Some say that two layers is the best way... I.E. putting down glue, then letting it tack, and then adding ANOTHER coat on top of that and letting it tack also is stronger than just one layer. Seems like overkill to me, but if you have trouble you can try it.
As far as gluing too much, don't sweat it. You can peel the turf up and clean the excess glue off with adhesive remover. Its not permanent.
Remember, its 'contact cement' so the strong bond is where you have glue on two separate surfaces that has 'tacked up' and you stick them together. Thats where the strongest bond happens. You may already know that, but if not...