Rewarded admob advertisements take too long to load

I have doubts in admob Rewarded, when I post it in the play store it takes 1 hour to work and the advertisements appear. I tried to make an adaptation using the admob Interstitial that does not happen this problem, but with it there is the problem of closing the application after seeing the advertisement, but this only happens in the play store because in Apk mode it does not happen. Has anyone ever experienced this ? Any suggestion ?