Nicky:
My best is pretty crap but I am just starting so I guess it doesn't count: 2mins. I've only been doing statics for a week so shut up! What is your best?

that's not bad!, I heard of much worse starters, and most people I know probably can't hold their breath a minute and half to save their lives.
When I started I was glad that I still have all my records infront of me. I still feel that way, since I'm also fairly new. and lazy.
My NEW best is 5:34 dry, done today. Before that it was 5.
And about substitute for dynamics, it depends on your goal, or the things you want to improve (your weak spots). I think that the most common practice for dynamics is apnea walking, or apnea stairwalking, some even do apnea whight lifting - which I'm against.
Just take it easy, you would'nt wanna have a smaba on the stairs, or for that matter, anywhere.
Keep going, and keep reading also

, there are tons of useful information on DB.