An easy rule to follow is 10-14 days, however, it is more important to watch the ratio of Reach to Impressions (aka Frequency) over the course of time your ad runs.
If at the end of 14 days your ad’s Reach to Impressions ratio is nearly 1:1, then every driver who has viewed your ad has only seen it once. If that is the case, you’re in a safe place to keep that ad live. It often takes a minimum repetition of 3 times for a driver to take action based on a message presented to them.
On the other hand, if at the end of 14 days your ad’s Frequency is 3 or more, consider starting a new ad with a different copy or creative since that particular message has had a reasonable chance to drive action among drivers.
We recommend logging into the platform every day or two in order to check on your ad’s activity and make decisions accordingly.