Assessment Center - Postopone or Not????

#1

I was invited to attend the AC with big top consultancy. I can’t make it to the first scheduled one - the next one being scheduled for later in the month. The recruitment manager told me on the phone that they would prefer if I could make it to the first one and he sort of hinted that leaving it to the next one lessens the chances of getting the offer since they will be making offers straight away. He then told me in an e-mail that its OK if I can’t make it - they will just schedule me for the next one. What would you do - go to the first one (meaning I have to fly back to London from my holiday, book additional flights and miss out on a big family matter I have to attend to), or just wait until the next one. Will it be seen as lack of enthusiasm, or lack of interest on my side, if I don’t go to the first one?
Many thanks.