I've been once on a weekend and it seemed hellish, but I had just come back from Bolivia and it had been a 2 day trip already. My mum thought the best antidote to my tiredness was shopping! 
Normally I'd go on a weekday. DP and I once got there about 10ish and even carrying around my big bump it was fine.
As long as you've got a brolly (and sharp elbows if it's a weekend) it'll be fine! 