I worked in a large Thai company and we had to make work plans for the next 6 months/year and they used a range of 6 months for the timeframe. Normally, I have to say, they hit it spot on in the middle of the range. Common PM techniques do this as part of common project management in the form of best case, most likely and worst case estimates - perhaps it make sense to implement this in all aspects of estimating timeframes in this country, I agree with above, there is no point to get frustrated with the way it is here, it will just make you grey haired early and you will look like me!!

Go with the flow, do it the Thai way and say 'mai pen rai' is best.

Is the company you are with Thai or foreign run?

I have worked for a few foreign run companies here and they often end up hitting their heads against brick walls for reasons like this.

When in Thailand, you simply have to do it their way, there is no point thinking things will be done as they are in your country and if the company is run by Thais they are taking estimates given to them by other thais with a pinch of salt because they know very well that things simply do not happen the way they're planned. T.I.T...!