Jurors are normally required to attend for 5 days per week, for a fortnight. (Courts normally sit from 10.00a.m or 10.30a.m. Jurors will be required to be there earlier but, because jurors are selected from a pool, they may not be required on some days). The court adjourns for lunch and, after resuming, continues until the judge decides it's convenient to close proceedings for the day. This is often around 4.00p.m. or 5.00p.m.but could be earlier or (rarely) later.
The average length of a trial is one and a half days. Some trials are shorter, so it's possible that jurors might be called to sit on two (or more) trials in a day. However, quite a few trials last a week or longer. A small number of trials can take many months. (The Operation Crevice trial was scheduled for 6 months of court time but lasted over a year. The jury took 27 days to decide their verdicts:
http://business.timesonline.co.uk/tol/business /law/article1728811.ece ). With such trials, the jury have to attend for however long the case takes.
For further information, click through the links here:
http://www.cjsonline.gov.uk/juror/jury_service /index.html
Chris