sometimes there are no signs, or it happens so quickly we don't realize it. This recently happened to Meowzer.
Most of the time, you'll start to see the mouth spread out and then start to separate.
YUP...took a couple of days and then there were 2..LOL
I have read some threads though where it takes a week or 2.....I had never had one split before, so I can tell you this....when it is happening, you will know