Sometimes you might find that the ads don’t display usually because your budget isn’t high enough to get full search coverage.

For example

• Your ads are scheduled to display from 6am – 12 midnight, 7 days per week.
• Your budget is set at $20 per day

Scenario

Your ads are clicked a number of times from 6am – 12 midday and half of your budget is now used up so you only have $10 left of your daily budget. Your campaign still needs to run for 12 more hours so your ads will display intermittently throughout the rest of the day to give you the greatest coverage for the remainder of your scheduled ad time.

I’m assuming that Google does this so that you get an even level of enquiries throughout the day instead of lots of enquires all at once plus to minimise the same people looking for services from clicking your ads multiple times.