RE: 5 x 5 - time in gym
Personally, I wouldn't worry about it unless you're spending 2 hours or longer in the gym doing the actual workout(not counting warmup & stretching).
Right now I'm doing 4 exercises per day(M/W/F) 3x8 and I take about 3 minutes in between sets. With warmups & stretching included, I usually finish up within just under an hour. I'll be starting the 5x5 routine in 5 weeks.
I don't think its mandatory to take 5 minutes in between every set, just rest until you feel recovered. But if you need 5 minutes, it shouldn't be a problem. If you're only doing 3 exercises(which is what you should be doing), then it shouldn't take you longer than 1 hour & 45 minutes to complete your workout, and that's including the time it takes you to warm up & stretch. Imo, that amount of time isn't going to hurt.
Now if you're trying to do 4 exercises, you're cutting it close & probably have to cut the rest period short in between some of your sets. I would think 4 is pushing the limit for 5x5, but you could probably get away with it on 4x6.
Some people spend too much time warming up, too. I do a quick 5 minute cardio warmup, stretch, do 1 warmup set on each exercise, stretch again, and then start my workout. Plain & simple. It doesn't take me longer than 10 minutes to warmup & get started.