Barons War is a good little game hidden inside a badly written rulebook.
To be fair though, most wargames rules are badly written.
It takes a while to get at what the rules writer meant (and to be fair to Andy Hobday he is EXTEMELY good at replying to emails and clarifying. Second to none, bless 'im).
But when you've winkled it all out you realise what an enjoyable, and simple, game it is.
On to your question.
Barons War doesn't scale that well. That's OK though, it only claims to be a skirmish game. The rules suggest games of 500 to 1000 points, and I'd say that's right. We once tried a 1500 point game and it lost something.
We find that we can get three 500 games in a whole day's worth of gaming. Or two 750 point games, or one 1000 point game. To give that some numbers, I'd say (on average) a 500 point game is done in between 1 or 2 hours. A 750 point game in 2 or 3. And 1000 in 3 or 4.
That kind of thing. It will all depend on how well you all know the rules and how the game goes - if you all know what you're doing you'll be at the low end of those figures (a few weeks ago we had a 500 point game that was done in half hour! That was mainly due to a truly catastrophic, and untypical, round where I was rolling very badly).
If you are introducing the game to new players, and you want them to enjoy it and want to play more, then I'd say that you need to ensure you know the rules because if you need to check something mid-play then it can take a while because some rules are just randomly scattered throughout the rulebook and you'll not find them in a timely manner and it can get frustrating.
Like I say, a good game, but badly written and laid out (looks great though, eh!).
So just make sure you know what you're doing first or else your fellow gamers may come away unimpressed.
But once you do know what you are doing then you'll really enjoy it.
Just like Chain of Command.