Wait how does this make sense? If 80% needed 23 months then only 20% are different (shorter or much longer!). What do you mean most are shorter?
80% (from that time period of submission) took X weeks or less. It is not an average, it is not a median.
Hence 80% (minus one) took less than that number of weeks. Some of them quite a bit less.
20% take/took longer.