I don`t think so (don`t quote me though). You just turn up. I can`t imagine you would have any problem climbing when you want to. If you look at the bridge, there are always 4 or 5 groups climbing at any one time. Normally, you don`t even need to book. Good idea not going too early in the morning as they breathalise you and I know a few people who have been turned away because they had a few sherberts the night before.
Maybe its got 'easier' to do since I did it in 2008, but we had to book quite a way in advance and you certainly couldn't 'just turn up' for any of the climbs. Its very good though and an easy climb...very few 'vertical' bits. Tremendous view from the top too.
Yes you can - you start off by saying you want (eg) daytime and it then offers you a choice of specific times that are available for you to choose and book
I think I called up to see if there was space and then just went the same day. It's really good fun, the worst bit is actually going up/down the ladder thingys to get on the bridge, I hate them. Once on the bridge it's ace. The evening one is supposed to be great. I did mine late afternoon I think.