Unless the 17.55 looks absolutely chocker, the answer has to be stay put!

If you can't make the earlier AMS flight then you will end up on the 17.55 more or less automatically if you are delayed and its one PNR. If it's 2 tickets and it's BA's fault it is almost certain they will rebook you without fuss anyway. And there are services after that too.

90 minutes is perfect connecting time in my book, I do that sort of connection more or less daily at T5.