This is what I got from one of the memes who shall remain nameless:
"Hi there, I have noticed you sending multiple emails in regards to memes waiting in approval and thought it might be useful to provide some more context. Many images on Imgflip are automatically approved; the automated system looks at multiple factors including what templates are used, text, inclusion of custom images, relative contentiousness of other content on a given stream, previous user behavior etc. If the system can't be certain a meme should be featured it is sent to an approval queue which is manually accessed by global and site moderators to clear. The queue is checked twice per day as an absolute minimum; the number is usually at least 4 times daily. If your meme happens to be created just after the queue has been cleared, it may wait in queue for comparatively longer; similarly if it is created just before the queue is cleared, it will not wait for very long. I hope this is helpful."