Most labs work monday to friday, but most supervisors like you to put in some time over the weekend. It depends on your workload and how quickly you want to finish your PhD. One nice thing about working in a lab is that your hours are flexible...one day might be 9-3 another it might be 9-8.
As for holidays PhD students are usually allowed between 4 and 8 weeks off, but what your allowed by the university and what your supervisor will want you to have off may be a different matter.