The amount of time it takes to smoke brats can vary a little depending on how many brats you are smoking and the size of them. For example, lots of very thick brat sausages may take a little longer to smoke than thin brat sausages.
That being said, it is possible to estimate roughly how long it will take to smoke your brats. Typically you can expect them to take anywhere between 45 minutes to 1 hour. Bear in mind that this time estimate is for a smoker that is set to 250 degrees Fahrenheit.
If the temperature is lower than this then it will take longer for them to be smoked. Likewise, if the temperature is set higher than the time it takes it may well be quicker.
However, any higher than 250 degrees Fahrenheit and the brats are likely to be over smoked and less palatable than if they are cooked slower and at a lower temperature.