Each time the error comes up, the timer resets.
For example:
You post.
You try to post again but only 19 seconds have passed.
Error comes up, resetting the timer.
You try again in 5 seconds, thinking "oh this should be 20 seconds now" only to have the error show up because only 5 seconds have passed. Resetting the timer again.
You just gotta wait 20 seconds after the last time you got an error.