Am I understanding correctly that you know how to figure out the probability of somebody waiting less than a certain time, but not how to figure out the probability of them waiting MORE than a certain time?
First find the probability of waiting less than an hour. Everybody waits either more than an hour, or less than an hour. Important concept: the sum of the probability of all outcomes is always going to be 1 (in technical language, the distribution is normalized). So just subtract your probability of waiting less than an hour from one, and you have the answer.
An alternative approach is to notice that the normal distribution is symmetrical around the mean, so the probability of waiting more than 1 hour is the same as the probability of waiting less than 30 minutes (both are 15 minutes from the mean).