You most probably have a limited daily advertising budget. Therefore, Google & Bing try to distribute your budget throughout the day. Otherwise you would only have a few clicks in the morning and you would reach your daily budget by the early morning. This wouldn’t give space for time optimisations: are people signing up more in the afternoon ? Late at night?
Given this distribution throughout the day, your ads are not triggered every time a user is searching for your keywords.
So bad luck, it didn’t show up when you tried to see your ad.