Rosie,
As far as I remember, the first week does include some classes and lots of important info, so i'd say it's definitely important to attend, i'm pretty sure class registers had to be signed during the first week too.
I'd just finished full time work too, when i started nursing, in fact i only got my place less than 2 weeks before the start of the course - my manager was really understanding about the short notice, thankfully!