aliu sc
I had a similar problem for my Stage 2. I was unavailable for a month as I was out of the country getting married. Just ring HR and explain. They told me that if you don't book your next stage after a certain time they assume you're no longer interested and withdraw your application but if you ring 'em and explain they'll just put your application 'on hold'. You then ring back when you're available and they update your records accordingly.
Good luck.