sharepoint online – CSOM: How do I know if a website has finished creating?

I have a service that creates a Sharepoint Online site with the help of CSOM.

context.Web.Webs.Add (webCreationInformation);
context.ExecuteQuery ();

This site is created with the help of a defined template stored in the site collection solutions. However, the creation of the site can take time: from 5 minutes to 20 minutes for the site to be ready (all created lists, all views, etc.), because my ExecuteQuery always returns to 5 minutes (usually with an error 503) It's impossible for me to know when the site has completed the creation process.

Is there a way to know when the site is available?

I've tried to load the web object and even if it's not ready, I can load it without problems:

Web sourceWeb = context.Site.OpenWeb (webRelativeUrl);
context.Load (web source);
context.ExecuteQuery ();
// this returns the web even if the site has not completed the creation process

I would like to have something like:

While (! Web.IsReady)
Thread.Sleep (60000); // 60 seconds
context.Load (Web, w => w.IsReady);
context.ExecuteQuery ();

However, I can not find a flag or value that can help me for that.

Thank you.