We went on a wednesday morning recently as were told weekends are too busy. Got there in time for opening at 11am. There was a queue- about maybe 50/60 people, but the shop is so massive that once you get in you don't notice. We knew what we were going for- about 4/5 items so we were out in our car by 12 noon. If I had lingered I would have bought a lot more so it's just as well to get in and out quickly.
Weekday evenings (Mon - Thur) after 6 are the best time to go in my opinion, much quieter and you sometimes have parts of the shop all to yourself and the restaurant is also very quiet too.
Weekends are way too busy I made that mistake a couple of times. Now I pop in on an evening mid week about 6pm (dinnertime for most) and it's no bother to get in and out quickly. Also you don't have to walk through all the show rooms etc if you have the code for the products you want so that would save you time.
I live about 15/20 minutes away and, the last time I needed something there, was up and back inside about 90 minutes. At 7:30 / 8:00 PM, there's not too many others around.
i usually go in the afternoon, between 2.30 - 3.30 and has been really quiet, kids being picked up in school etc and between 6.30 7.30 dinner time has been very handy also and can park really close