and after certain number of times I got an error message:
There were too many requests of a given type :: Error creating new cert :: Too many certificates already issued for exact set of domains: mydomain.org,www.mydomain.org
i.e. if a 1st command was at Monday and last command was at Wednesday (when limit is occur) then I can issue the next certificate at next Monday, isn’t it?
For my curiousity, why did you run the command, with --renew-by-default, so many times?
If you are experimenting or testing stuff, it's wise to add the --staging switch to your certbot command. This will give you "fake" (i.e., give an SSL error in client browsers), but otherwise (in te context of webservers) working certificate. The staging server doesn't have such rate limits (not as low at least), so you can experiment and test whatever you like!
And when you're done testing, you can remove the --staging switch to get the final, working certificate.