Dynamic Search Ads

I'm running these in various account and cannot understand when exactly it starts running.
In some campaigns it takes hours and in others it can take a couple of days!

Does anybody have an input as to why it happens?

 

It is based on the priority of accounts and ads creation.
Whenever you create an ad, Google reviews the ad to make sure that it complies with our advertising policies and is safe and appropriate for users.

Team Adwords review ads as quickly as possible, and they review most ads within 1 business day. Some reviews may take longer because some ads require more complex review.

Accounts generally get scheduled in Round Robin Format. May be the person handling your one account is free and other account is busy and that is why it takes few hours and a day to get it checked.

Hope you find this useful.

 

When running campaigns with a daily budget of over 1000$, ads get approved in a couple of hours...
the ads are approved in a couple of hours in these campaigns as well.

The question was, why does it take so long for them to start displaying

 

It is depending upon your targeting methods..lets say, you are using dynamic ads for A campaign and you are targeting keywords that is not largely searched by audiences, it may show when your targeting method match.

Apart from this, you might have multiple ads for same adgroups and Google adwords shows different ads to test the best converting ad. Here it takes time in scheduling !