Don't waste any of your Graduated Resettlement Time, or the grant/money that comes with it.
Think 4 months is too tight to pack everything in. Does the new job outweigh the GRT?
Congratulations by the way in being offered a job - this tells me right from the off you are a person with immediate employable skills and ability and this is brilliant start to a new life-but are you sure you want to rush out to it (the first job offered) and not use what is rightfully yours??
And when you go, it is a rush and a little bit stressful ( I found the money side of it with JPA difficult to get a grip with until friendly Naval admin helped me with it).
But good luck either way.