How long must I wait for google to send a mail whose title is "Mobile-first indexing enabled" after I optimizing my official site "Mobile-Friendly"?

How long must I wait for google to send a mail whose title is "Mobile-first indexing enabled" after I optimizing my official site for Mobile-Friendly?

We sell a service called "Competitive Analysis". In this service, we sometimes have to suggest to clients how often they need to use the service. So, September in 2018, we decided to investigate how long must we wait for google to send a mail whose title is "Mobile-first indexing enabled" after we optimizing our official sites ( all subdomains on Rainbow-Link.com ) for Mobile-Friendly.

First, we want to talk about the premise. Till July in 2018, because we had denied crawler bots to access stylesheets at robots.txt, we knew that if we denied google bot to read stylesheets, we could obtain high score at "Mobile-Friendly Test", and google ranked our pages by using pages in our PC site. And, since July in 2018, because we didn't optimize our official site for mobile - we knew that even app users rarely visit the official site because we had launched some smartphone apps at google & apple app stores -, google ranked our sites low, and, we recognized that we had to optimize our sites for mobile in order to do SEO. So, to begin this experiment, we rewrote our robots.txt to let google bot read all stylesheets at our official sites. Then, google bot indexed page 50 of 130 we sent via sitemap. So, we put '50 pages' as a base number, and we decided to view the number of indexed pages by google.

See the Figure 1. Sep 15, 2018, we modified stylesheet to NO-scroll if visitors accessed via mobile. Then, from the end of Sep to the end of Oct, 2018, google indexed only 16 pages. We could confirm that at "Mobile Usability" at google search console. So, we found that at "Mobile Usability" at google search console, google had read not only HTML, but also stylesheets to determine whether the page has been optimized for mobile. We reckoned that google smartphone bot determined whether the page has been optimized for mobile by reproducing the "state when people actually access and browse via mobile". We haven't used the javascript at our official website, but, if we have used javascript, google would have use javascript in order to determined whether the page has been optimized for mobile.

Because we recognized that google had read not only HTML, but also stylesheets to determine whether the page has been optimized for mobile, Oct 30, 2018, we modified stylesheets again. This time, we modified stylesheets to ON-scroll if visitors accessed via mobile, and we added a menu-button that couldn't launch if visitors accessed via iPhone's safari. We reckoned that the google's base of "Mobile" was "Android".

However, the result was to betray our expectations. See the Figure 1. Google didn't re-index our pages at official site to the level of before Aug 2018. So, we recognized that google's "mobile" meant not only Android but also iPhone.

Then, in order to confirm the point 'google's "mobile" meant not only Android but also iPhone', Dec 20, 2018, we took the "Mobile-Friendly Test". The result of the test was the Figure 2. I want you to see the part that drew the red line of Figure 2. That was a part we displayed for only accesses via iPhone by using distributing browsers in our web-servers. So, we could confirm that google's "mobile" meant not only Android but also iPhone.

Then, because we finished confirming the matters we wanted to know about "Mobile-Friendly", Dec 20,2018, we submitted the Crawl Application at google search console. Jan 11, 2019, google sent a mail whose title was "Mobile-first indexing enabled" to us. So, we could know that we must to wait for google to send a mail whose title is "Mobile-first indexing enabled" after we optimizing our official site "Mobile-Friendly" for 22 days.

Figure 1

Figure 2