Google has updated its help page to specify ad review times for different campaign types. Most reviews are completed within one business day, but standard reviews for Demand Gen and Discovery campaigns now take 3-5 business days, with complex formats potentially requiring up to 7 days.
Advertisers are advised to avoid making edits to budgets, bid strategies, or ad text while an ad is under review, as any modification resets the review clock. If the review status hasn’t changed after 7 business days, a minor edit can trigger the review process again.

These changes highlight the need for advertisers to carefully plan their campaigns around these review timelines to ensure timely ad activation.
Read the official help page here: Check the review status of an ad or asset.
This update was spotted by Hana Kobzová.