I am wondering how long do we have to be online, before we don't have to be online with steam?
If you are asking how long it will take to down load the first Alpha build, try this formula:
total code size <they said 1.8G> * 8 <convert from bytes to bits> / (your suppliers rated speed <if not reduced upstream> * 90% <delivery overhead>) / 60 <convert seconds to minutes> --- Of course, your results may vary.