I've just had a molar capped. before he put the cap on my tooth, i touched it with my tongue. how long will it be before the abscess arrives?

Hopefully never1: A tooth will not abcess just because you touched the exposed tooth with your tongue. If you needed a crown, then there is obviously a lot of damage to the tooth and that can lead to further complications. Contact your dentist and he/she will be happy to explain your specific situation.

Maybe never: A tooth abscesses because the "nerve" dies. On average, 11% of teeth that have crowns will later need a root canal. You needed the crown because of large fillings covering more than 70% of the surface of the tooth, or large cavity or broken cusp. Talk to your dentist about your concern.