For a first half I'd avoid thinking about time that much. One thing to check, however, is the time limit that the race has; some races will pick you up if you are not at a certain point in the course by a certain time.
For training I used Hal Higdon for my first half. He even has a training program for walking it - www.halhigdon.com/training/51134/Half-Mara
Edited by: SUSAN_FOSTER at: 2/24/2013 (14:03)