ios app waiting for review how long?

It lasts … some time.

No one can predict.

I keep statistics on this, and it varied (for updates) from hour to 2 weeks.

So, just be patient.

The exact wait is indeterminate, and can only be judged by Apple's stats. and anecdotal reports from other devs.

The question is often asked, and the answer is always the same - be patient, and watch your mail for status notifications/rejections etc. from App Review.

https://developer.apple.com/app-store/review/

"Review Status

Once you’ve submitted your app for review, you can view its status in the My Appssection of App Store Connect or on the App Store Connect App for iPhone and iPad. Review times may vary by app. On average, 50% of apps are reviewed in 24 hours and over 90% are reviewed in 48 hours. If your submission is incomplete, review times may be further delayed or your app may be rejected. Once your app has been reviewed, its status will be updated and you will be notified.

For more details, see App Store Connect Help."