I know that for Ads and Landing pages there should be at least 30 actions, clicks, conversions etc., if there is a big difference in the results, if there is not much difference, one should wait for 50 or even 100 clicks. I can also use some splittest tools for this.
But what is the rule of thumb for keywords? I cannot wait for 30 clicks for each keyword, if I just want to try 100 or more keywords, just to see which ones have the best CTR.
And if there are 200 impressions and no clicks, I pause the KW and it is not statistically significant, maybe later the same KW would perform much better.