Looking to play some games of Brass online but have never played any games by email.
One question that I have is do most games play about the same amount of time or do they take longer?
In other words do people sit and play a full game or do they come back and check much later to take there turn?

Depends very much on who you are playing. But in general, people are not standing by to take their turn. If you're lucky (assuming you want to play fast), you'll get in a few turns a day.

My suggestion is to start your own 2 or 3 player game and mark the 'friendly' check box, just to get your feet wet. You can set time outs to your preference (there's a player vote kick-out and a hard system kick-out). The game will fill up very quickly and you'll be on your way. Jump on in - the water's fine.