That will depend on when you folks start the exam in the morning. It is normally scheduled for starting at 8am; 4 hour session, 1 hour lunch and resume immediately upon everyone showing up after lunch. As the morning starts out, if there are stragglers or a proctor that wishes to take their time reading the rules, it can be delayed by about 15 minutes. If you think you'll be taking the full 4 hours, and should there be the typical delays; don't be expecting to leave before 5:30 pm.
Best advice I can give, is to get there and be ready to go in when they open their doors for the day. This only works for yourself as they're will normally be someone who shows up late.
Good luck on your exam.