DVC is one of the few ( if only) low pressure timeshare sales. Actually I would say there is no pressure at all.
You can take as much, or as little time as you want. BUT IMHO if you want to get a good feel for the product you need to set aside a couple of hours. When we went round they had a creche to look after the kids, so they were happy and we could concentrate on the job at hand.
It's certainly a good idea to do as much research as you can before going, if you have the time you can call them fromt he UK and ask to be sent a DVC video ( specify you need it to be in UK format, I know that should be obvious to them as it's being posted to the UK, but sometimes the agents are not aware we have a different video format). That way you can go over some of the information at home, at your own pace. It will give the chance to formulate questions that are particular to your requirements.
Like Stephen, I thought it was too good to be true and spent quite a while looking for the catch, but that was in 1993 and I'm still looking for it LOL.
The only way to get a feel for the units is by going through the tour and walking through the units. The studio isn't hard to visualise, it's pretty much a standard hotel room size, but the larger units need to be seen.
If you're coinsidering a timeshare in the Orlando area, then IMHO the DVC tour is a must do, even if you decide not to sign up, for whatever reason, you can feel you've done so knowing all the facts.