Know the Speed that People Read Blog Posts
It takes an average person 1 minute to read about 150 words so why not take this into account when placing an email opt in pop-up form on your site.
choosing the Best Time for Your Pop up Form To Appear
First you will need to know the average amount of words for each post on your blog if you are unsure install the estimated reading time plugin for WordPress view some random blog posts and work out your blog post word count average.To Work out your Estimated reading time you may need to Download the Estimated Reading Time Plugin for WordPress .The plugin is not necessary to keep installed once you have your average blog post word count but you may want to keep it for some other reason.
Optin Forms are Useless Without Targeting.
If you place a optin form for a make money system on a page that is showing a tutorial on fixing your laptop your visitors will see it as irrelevant to your text anyway especially if it loads when they are reading your content and want to get their computer problem solved. They will become distracted and leave your page instantly pop up forms are as annoying as these pop ups that appear on sites 
Give Visitors Time To Read Before Asking To Optin
After taking into account the time you want your opt in pop up to load you do not want a pop-up loading when visitors are reading an article so your pop up delay time should be set either for the second page view or when visitors have read the article for example if your blog post was 300 words that would take 2 minutes to read depending on the text. So setting your pop up to a 120000 ms delay will allow your visitors to read the content and then decide to opt in to your list and not just close your pop up and go back to the search results page on Google.This will help in gaining Target email subscribers for Email Newsletters that result in higher open rates and more sales



