In reply to IainMunro:
as far as I know, tomorrow Easter Mon is 25th of April.
so it's 9am -6pm
26 March - April: 9am-6pm
If you go in May then it's
May: 9am-7pm
Thus one hour longer in May
See below
Summer access this year is from 26 March to 31 October, and is controlled by a gate-keeper:
26 March - April: 9am-6pm
May: 9am-7pm
June: 9am-8pm
July: 9am-8pm
Aug: 9am-8pm
Sept: 9am-7pm
Oct: 9am-6pm