In order to let EasyCron use your new IP immediately, you can
For example, if your cron job URL is https://www.example.com, your new IP is 126.96.36.199. You should add https://188.8.131.52 as cron job URL, and in the "HTTP" tab -> "HTTP headers" field, add Host: www.example.com.
In this way, EasyCron will use your new IP (and the domain name) to connect to your website and your cron job will work immediately even your new DNS records still haven't finished propagation.
After your new DNS records are fully propagated, you can change your cron jobs to normal format. Using the example above, that is, changing https://184.108.40.206 to https://www.example.com and removing the "Host: www.example.com" header.